FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/zcp.c

     /*
      * CDDL HEADER START
      *
      * This file and its contents are supplied under the terms of the
      * Common Development and Distribution License ("CDDL"), version 1.0.
      * You may only use this file in accordance with the terms of version
      * 1.0 of the CDDL.
      *
      * A full copy of the text of the CDDL should have accompanied this
     * source.  A copy of the CDDL is also available via the Internet at
     * http://www.illumos.org/license/CDDL.
     *
     * CDDL HEADER END
     */
    
    /*
     * Copyright (c) 2016, 2018 by Delphix. All rights reserved.
     */
    
    /*
     * ZFS Channel Programs (ZCP)
     *
     * The ZCP interface allows various ZFS commands and operations ZFS
     * administrative operations (e.g. creating and destroying snapshots, typically
     * performed via an ioctl to /dev/zfs by the zfs(8) command and
     * libzfs/libzfs_core) to be run * programmatically as a Lua script.  A ZCP
     * script is run as a dsl_sync_task and fully executed during one transaction
     * group sync.  This ensures that no other changes can be written concurrently
     * with a running Lua script.  Combining multiple calls to the exposed ZFS
     * functions into one script gives a number of benefits:
     *
     * 1. Atomicity.  For some compound or iterative operations, it's useful to be
     * able to guarantee that the state of a pool has not changed between calls to
     * ZFS.
     *
     * 2. Performance.  If a large number of changes need to be made (e.g. deleting
     * many filesystems), there can be a significant performance penalty as a
     * result of the need to wait for a transaction group sync to pass for every
     * single operation.  When expressed as a single ZCP script, all these changes
     * can be performed at once in one txg sync.
     *
     * A modified version of the Lua 5.2 interpreter is used to run channel program
     * scripts. The Lua 5.2 manual can be found at:
     *
     *      http://www.lua.org/manual/5.2/
     *
     * If being run by a user (via an ioctl syscall), executing a ZCP script
     * requires root privileges in the global zone.
     *
     * Scripts are passed to zcp_eval() as a string, then run in a synctask by
     * zcp_eval_sync().  Arguments can be passed into the Lua script as an nvlist,
     * which will be converted to a Lua table.  Similarly, values returned from
     * a ZCP script will be converted to an nvlist.  See zcp_lua_to_nvlist_impl()
     * for details on exact allowed types and conversion.
     *
     * ZFS functionality is exposed to a ZCP script as a library of function calls.
     * These calls are sorted into submodules, such as zfs.list and zfs.sync, for
     * iterators and synctasks, respectively.  Each of these submodules resides in
     * its own source file, with a zcp_*_info structure describing each library
     * call in the submodule.
     *
     * Error handling in ZCP scripts is handled by a number of different methods
     * based on severity:
     *
     * 1. Memory and time limits are in place to prevent a channel program from
     * consuming excessive system or running forever.  If one of these limits is
     * hit, the channel program will be stopped immediately and return from
     * zcp_eval() with an error code. No attempt will be made to roll back or undo
     * any changes made by the channel program before the error occurred.
     * Consumers invoking zcp_eval() from elsewhere in the kernel may pass a time
     * limit of 0, disabling the time limit.
     *
     * 2. Internal Lua errors can occur as a result of a syntax error, calling a
     * library function with incorrect arguments, invoking the error() function,
     * failing an assert(), or other runtime errors.  In these cases the channel
     * program will stop executing and return from zcp_eval() with an error code.
     * In place of a return value, an error message will also be returned in the
     * 'result' nvlist containing information about the error. No attempt will be
     * made to roll back or undo any changes made by the channel program before the
     * error occurred.
     *
     * 3. If an error occurs inside a ZFS library call which returns an error code,
     * the error is returned to the Lua script to be handled as desired.
     *
     * In the first two cases, Lua's error-throwing mechanism is used, which
     * longjumps out of the script execution with luaL_error() and returns with the
     * error.
     *
     * See zfs-program(8) for more information on high level usage.
     */
    
    #include <sys/lua/lua.h>
    #include <sys/lua/lualib.h>
    #include <sys/lua/lauxlib.h>
    
    #include <sys/dsl_prop.h>
    #include <sys/dsl_synctask.h>
    #include <sys/dsl_dataset.h>
    #include <sys/zcp.h>
   #include <sys/zcp_iter.h>
   #include <sys/zcp_prop.h>
   #include <sys/zcp_global.h>
   #include <sys/zvol.h>
   
   #ifndef KM_NORMALPRI
   #define KM_NORMALPRI    0
   #endif
   
   #define ZCP_NVLIST_MAX_DEPTH 20
   
   static const uint64_t zfs_lua_check_instrlimit_interval = 100;
   uint64_t zfs_lua_max_instrlimit = ZCP_MAX_INSTRLIMIT;
   uint64_t zfs_lua_max_memlimit = ZCP_MAX_MEMLIMIT;
   
   /*
    * Forward declarations for mutually recursive functions
    */
   static int zcp_nvpair_value_to_lua(lua_State *, nvpair_t *, char *, int);
   static int zcp_lua_to_nvlist_impl(lua_State *, int, nvlist_t *, const char *,
       int);
   
   /*
    * The outer-most error callback handler for use with lua_pcall(). On
    * error Lua will call this callback with a single argument that
    * represents the error value. In most cases this will be a string
    * containing an error message, but channel programs can use Lua's
    * error() function to return arbitrary objects as errors. This callback
    * returns (on the Lua stack) the original error object along with a traceback.
    *
    * Fatal Lua errors can occur while resources are held, so we also call any
    * registered cleanup function here.
    */
   static int
   zcp_error_handler(lua_State *state)
   {
           const char *msg;
   
           zcp_cleanup(state);
   
           VERIFY3U(1, ==, lua_gettop(state));
           msg = lua_tostring(state, 1);
           luaL_traceback(state, state, msg, 1);
           return (1);
   }
   
   int
   zcp_argerror(lua_State *state, int narg, const char *msg, ...)
   {
           va_list alist;
   
           va_start(alist, msg);
           const char *buf = lua_pushvfstring(state, msg, alist);
           va_end(alist);
   
           return (luaL_argerror(state, narg, buf));
   }
   
   /*
    * Install a new cleanup function, which will be invoked with the given
    * opaque argument if a fatal error causes the Lua interpreter to longjump out
    * of a function call.
    *
    * If an error occurs, the cleanup function will be invoked exactly once and
    * then unregistered.
    *
    * Returns the registered cleanup handler so the caller can deregister it
    * if no error occurs.
    */
   zcp_cleanup_handler_t *
   zcp_register_cleanup(lua_State *state, zcp_cleanup_t cleanfunc, void *cleanarg)
   {
           zcp_run_info_t *ri = zcp_run_info(state);
   
           zcp_cleanup_handler_t *zch = kmem_alloc(sizeof (*zch), KM_SLEEP);
           zch->zch_cleanup_func = cleanfunc;
           zch->zch_cleanup_arg = cleanarg;
           list_insert_head(&ri->zri_cleanup_handlers, zch);
   
           return (zch);
   }
   
   void
   zcp_deregister_cleanup(lua_State *state, zcp_cleanup_handler_t *zch)
   {
           zcp_run_info_t *ri = zcp_run_info(state);
           list_remove(&ri->zri_cleanup_handlers, zch);
           kmem_free(zch, sizeof (*zch));
   }
   
   /*
    * Execute the currently registered cleanup handlers then free them and
    * destroy the handler list.
    */
   void
   zcp_cleanup(lua_State *state)
   {
           zcp_run_info_t *ri = zcp_run_info(state);
   
           for (zcp_cleanup_handler_t *zch =
               list_remove_head(&ri->zri_cleanup_handlers); zch != NULL;
               zch = list_remove_head(&ri->zri_cleanup_handlers)) {
                   zch->zch_cleanup_func(zch->zch_cleanup_arg);
                   kmem_free(zch, sizeof (*zch));
           }
   }
   
   /*
    * Convert the lua table at the given index on the Lua stack to an nvlist
    * and return it.
    *
    * If the table can not be converted for any reason, NULL is returned and
    * an error message is pushed onto the Lua stack.
    */
   static nvlist_t *
   zcp_table_to_nvlist(lua_State *state, int index, int depth)
   {
           nvlist_t *nvl;
           /*
            * Converting a Lua table to an nvlist with key uniqueness checking is
            * O(n^2) in the number of keys in the nvlist, which can take a long
            * time when we return a large table from a channel program.
            * Furthermore, Lua's table interface *almost* guarantees unique keys
            * on its own (details below). Therefore, we don't use fnvlist_alloc()
            * here to avoid the built-in uniqueness checking.
            *
            * The *almost* is because it's possible to have key collisions between
            * e.g. the string "1" and the number 1, or the string "true" and the
            * boolean true, so we explicitly check that when we're looking at a
            * key which is an integer / boolean or a string that can be parsed as
            * one of those types. In the worst case this could still devolve into
            * O(n^2), so we only start doing these checks on boolean/integer keys
            * once we've seen a string key which fits this weird usage pattern.
            *
            * Ultimately, we still want callers to know that the keys in this
            * nvlist are unique, so before we return this we set the nvlist's
            * flags to reflect that.
            */
           VERIFY0(nvlist_alloc(&nvl, 0, KM_SLEEP));
   
           /*
            * Push an empty stack slot where lua_next() will store each
            * table key.
            */
           lua_pushnil(state);
           boolean_t saw_str_could_collide = B_FALSE;
           while (lua_next(state, index) != 0) {
                   /*
                    * The next key-value pair from the table at index is
                    * now on the stack, with the key at stack slot -2 and
                    * the value at slot -1.
                    */
                   int err = 0;
                   char buf[32];
                   const char *key = NULL;
                   boolean_t key_could_collide = B_FALSE;
   
                   switch (lua_type(state, -2)) {
                   case LUA_TSTRING:
                           key = lua_tostring(state, -2);
   
                           /* check if this could collide with a number or bool */
                           long long tmp;
                           int parselen;
                           if ((sscanf(key, "%lld%n", &tmp, &parselen) > 0 &&
                               parselen == strlen(key)) ||
                               strcmp(key, "true") == 0 ||
                               strcmp(key, "false") == 0) {
                                   key_could_collide = B_TRUE;
                                   saw_str_could_collide = B_TRUE;
                           }
                           break;
                   case LUA_TBOOLEAN:
                           key = (lua_toboolean(state, -2) == B_TRUE ?
                               "true" : "false");
                           if (saw_str_could_collide) {
                                   key_could_collide = B_TRUE;
                           }
                           break;
                   case LUA_TNUMBER:
                           (void) snprintf(buf, sizeof (buf), "%lld",
                               (longlong_t)lua_tonumber(state, -2));
   
                           key = buf;
                           if (saw_str_could_collide) {
                                   key_could_collide = B_TRUE;
                           }
                           break;
                   default:
                           fnvlist_free(nvl);
                           (void) lua_pushfstring(state, "Invalid key "
                               "type '%s' in table",
                               lua_typename(state, lua_type(state, -2)));
                           return (NULL);
                   }
                   /*
                    * Check for type-mismatched key collisions, and throw an error.
                    */
                   if (key_could_collide && nvlist_exists(nvl, key)) {
                           fnvlist_free(nvl);
                           (void) lua_pushfstring(state, "Collision of "
                               "key '%s' in table", key);
                           return (NULL);
                   }
                   /*
                    * Recursively convert the table value and insert into
                    * the new nvlist with the parsed key.  To prevent
                    * stack overflow on circular or heavily nested tables,
                    * we track the current nvlist depth.
                    */
                   if (depth >= ZCP_NVLIST_MAX_DEPTH) {
                           fnvlist_free(nvl);
                           (void) lua_pushfstring(state, "Maximum table "
                               "depth (%d) exceeded for table",
                               ZCP_NVLIST_MAX_DEPTH);
                           return (NULL);
                   }
                   err = zcp_lua_to_nvlist_impl(state, -1, nvl, key,
                       depth + 1);
                   if (err != 0) {
                           fnvlist_free(nvl);
                           /*
                            * Error message has been pushed to the lua
                            * stack by the recursive call.
                            */
                           return (NULL);
                   }
                   /*
                    * Pop the value pushed by lua_next().
                    */
                   lua_pop(state, 1);
           }
   
           /*
            * Mark the nvlist as having unique keys. This is a little ugly, but we
            * ensured above that there are no duplicate keys in the nvlist.
            */
           nvl->nvl_nvflag |= NV_UNIQUE_NAME;
   
           return (nvl);
   }
   
   /*
    * Convert a value from the given index into the lua stack to an nvpair, adding
    * it to an nvlist with the given key.
    *
    * Values are converted as follows:
    *
    *   string -> string
    *   number -> int64
    *   boolean -> boolean
    *   nil -> boolean (no value)
    *
    * Lua tables are converted to nvlists and then inserted. The table's keys
    * are converted to strings then used as keys in the nvlist to store each table
    * element.  Keys are converted as follows:
    *
    *   string -> no change
    *   number -> "%lld"
    *   boolean -> "true" | "false"
    *   nil -> error
    *
    * In the case of a key collision, an error is thrown.
    *
    * If an error is encountered, a nonzero error code is returned, and an error
    * string will be pushed onto the Lua stack.
    */
   static int
   zcp_lua_to_nvlist_impl(lua_State *state, int index, nvlist_t *nvl,
       const char *key, int depth)
   {
           /*
            * Verify that we have enough remaining space in the lua stack to parse
            * a key-value pair and push an error.
            */
           if (!lua_checkstack(state, 3)) {
                   (void) lua_pushstring(state, "Lua stack overflow");
                   return (1);
           }
   
           index = lua_absindex(state, index);
   
           switch (lua_type(state, index)) {
           case LUA_TNIL:
                   fnvlist_add_boolean(nvl, key);
                   break;
           case LUA_TBOOLEAN:
                   fnvlist_add_boolean_value(nvl, key,
                       lua_toboolean(state, index));
                   break;
           case LUA_TNUMBER:
                   fnvlist_add_int64(nvl, key, lua_tonumber(state, index));
                   break;
           case LUA_TSTRING:
                   fnvlist_add_string(nvl, key, lua_tostring(state, index));
                   break;
           case LUA_TTABLE: {
                   nvlist_t *value_nvl = zcp_table_to_nvlist(state, index, depth);
                   if (value_nvl == NULL)
                           return (SET_ERROR(EINVAL));
   
                   fnvlist_add_nvlist(nvl, key, value_nvl);
                   fnvlist_free(value_nvl);
                   break;
           }
           default:
                   (void) lua_pushfstring(state,
                       "Invalid value type '%s' for key '%s'",
                       lua_typename(state, lua_type(state, index)), key);
                   return (SET_ERROR(EINVAL));
           }
   
           return (0);
   }
   
   /*
    * Convert a lua value to an nvpair, adding it to an nvlist with the given key.
    */
   static void
   zcp_lua_to_nvlist(lua_State *state, int index, nvlist_t *nvl, const char *key)
   {
           /*
            * On error, zcp_lua_to_nvlist_impl pushes an error string onto the Lua
            * stack before returning with a nonzero error code. If an error is
            * returned, throw a fatal lua error with the given string.
            */
           if (zcp_lua_to_nvlist_impl(state, index, nvl, key, 0) != 0)
                   (void) lua_error(state);
   }
   
   static int
   zcp_lua_to_nvlist_helper(lua_State *state)
   {
           nvlist_t *nv = (nvlist_t *)lua_touserdata(state, 2);
           const char *key = (const char *)lua_touserdata(state, 1);
           zcp_lua_to_nvlist(state, 3, nv, key);
           return (0);
   }
   
   static void
   zcp_convert_return_values(lua_State *state, nvlist_t *nvl,
       const char *key, int *result)
   {
           int err;
           VERIFY3U(1, ==, lua_gettop(state));
           lua_pushcfunction(state, zcp_lua_to_nvlist_helper);
           lua_pushlightuserdata(state, (char *)key);
           lua_pushlightuserdata(state, nvl);
           lua_pushvalue(state, 1);
           lua_remove(state, 1);
           err = lua_pcall(state, 3, 0, 0); /* zcp_lua_to_nvlist_helper */
           if (err != 0) {
                   zcp_lua_to_nvlist(state, 1, nvl, ZCP_RET_ERROR);
                   *result = SET_ERROR(ECHRNG);
           }
   }
   
   /*
    * Push a Lua table representing nvl onto the stack.  If it can't be
    * converted, return EINVAL, fill in errbuf, and push nothing. errbuf may
    * be specified as NULL, in which case no error string will be output.
    *
    * Most nvlists are converted as simple key->value Lua tables, but we make
    * an exception for the case where all nvlist entries are BOOLEANs (a string
    * key without a value). In Lua, a table key pointing to a value of Nil
    * (no value) is equivalent to the key not existing, so a BOOLEAN nvlist
    * entry can't be directly converted to a Lua table entry. Nvlists of entirely
    * BOOLEAN entries are frequently used to pass around lists of datasets, so for
    * convenience we check for this case, and convert it to a simple Lua array of
    * strings.
    */
   int
   zcp_nvlist_to_lua(lua_State *state, nvlist_t *nvl,
       char *errbuf, int errbuf_len)
   {
           nvpair_t *pair;
           lua_newtable(state);
           boolean_t has_values = B_FALSE;
           /*
            * If the list doesn't have any values, just convert it to a string
            * array.
            */
           for (pair = nvlist_next_nvpair(nvl, NULL);
               pair != NULL; pair = nvlist_next_nvpair(nvl, pair)) {
                   if (nvpair_type(pair) != DATA_TYPE_BOOLEAN) {
                           has_values = B_TRUE;
                           break;
                   }
           }
           if (!has_values) {
                   int i = 1;
                   for (pair = nvlist_next_nvpair(nvl, NULL);
                       pair != NULL; pair = nvlist_next_nvpair(nvl, pair)) {
                           (void) lua_pushinteger(state, i);
                           (void) lua_pushstring(state, nvpair_name(pair));
                           (void) lua_settable(state, -3);
                           i++;
                   }
           } else {
                   for (pair = nvlist_next_nvpair(nvl, NULL);
                       pair != NULL; pair = nvlist_next_nvpair(nvl, pair)) {
                           int err = zcp_nvpair_value_to_lua(state, pair,
                               errbuf, errbuf_len);
                           if (err != 0) {
                                   lua_pop(state, 1);
                                   return (err);
                           }
                           (void) lua_setfield(state, -2, nvpair_name(pair));
                   }
           }
           return (0);
   }
   
   /*
    * Push a Lua object representing the value of "pair" onto the stack.
    *
    * Only understands boolean_value, string, int64, nvlist,
    * string_array, and int64_array type values.  For other
    * types, returns EINVAL, fills in errbuf, and pushes nothing.
    */
   static int
   zcp_nvpair_value_to_lua(lua_State *state, nvpair_t *pair,
       char *errbuf, int errbuf_len)
   {
           int err = 0;
   
           if (pair == NULL) {
                   lua_pushnil(state);
                   return (0);
           }
   
           switch (nvpair_type(pair)) {
           case DATA_TYPE_BOOLEAN_VALUE:
                   (void) lua_pushboolean(state,
                       fnvpair_value_boolean_value(pair));
                   break;
           case DATA_TYPE_STRING:
                   (void) lua_pushstring(state, fnvpair_value_string(pair));
                   break;
           case DATA_TYPE_INT64:
                   (void) lua_pushinteger(state, fnvpair_value_int64(pair));
                   break;
           case DATA_TYPE_NVLIST:
                   err = zcp_nvlist_to_lua(state,
                       fnvpair_value_nvlist(pair), errbuf, errbuf_len);
                   break;
           case DATA_TYPE_STRING_ARRAY: {
                   char **strarr;
                   uint_t nelem;
                   (void) nvpair_value_string_array(pair, &strarr, &nelem);
                   lua_newtable(state);
                   for (int i = 0; i < nelem; i++) {
                           (void) lua_pushinteger(state, i + 1);
                           (void) lua_pushstring(state, strarr[i]);
                           (void) lua_settable(state, -3);
                   }
                   break;
           }
           case DATA_TYPE_UINT64_ARRAY: {
                   uint64_t *intarr;
                   uint_t nelem;
                   (void) nvpair_value_uint64_array(pair, &intarr, &nelem);
                   lua_newtable(state);
                   for (int i = 0; i < nelem; i++) {
                           (void) lua_pushinteger(state, i + 1);
                           (void) lua_pushinteger(state, intarr[i]);
                           (void) lua_settable(state, -3);
                   }
                   break;
           }
           case DATA_TYPE_INT64_ARRAY: {
                   int64_t *intarr;
                   uint_t nelem;
                   (void) nvpair_value_int64_array(pair, &intarr, &nelem);
                   lua_newtable(state);
                   for (int i = 0; i < nelem; i++) {
                           (void) lua_pushinteger(state, i + 1);
                           (void) lua_pushinteger(state, intarr[i]);
                           (void) lua_settable(state, -3);
                   }
                   break;
           }
           default: {
                   if (errbuf != NULL) {
                           (void) snprintf(errbuf, errbuf_len,
                               "Unhandled nvpair type %d for key '%s'",
                               nvpair_type(pair), nvpair_name(pair));
                   }
                   return (SET_ERROR(EINVAL));
           }
           }
           return (err);
   }
   
   int
   zcp_dataset_hold_error(lua_State *state, dsl_pool_t *dp, const char *dsname,
       int error)
   {
           if (error == ENOENT) {
                   (void) zcp_argerror(state, 1, "no such dataset '%s'", dsname);
                   return (0); /* not reached; zcp_argerror will longjmp */
           } else if (error == EXDEV) {
                   (void) zcp_argerror(state, 1,
                       "dataset '%s' is not in the target pool '%s'",
                       dsname, spa_name(dp->dp_spa));
                   return (0); /* not reached; zcp_argerror will longjmp */
           } else if (error == EIO) {
                   (void) luaL_error(state,
                       "I/O error while accessing dataset '%s'", dsname);
                   return (0); /* not reached; luaL_error will longjmp */
           } else if (error != 0) {
                   (void) luaL_error(state,
                       "unexpected error %d while accessing dataset '%s'",
                       error, dsname);
                   return (0); /* not reached; luaL_error will longjmp */
           }
           return (0);
   }
   
   /*
    * Note: will longjmp (via lua_error()) on error.
    * Assumes that the dsname is argument #1 (for error reporting purposes).
    */
   dsl_dataset_t *
   zcp_dataset_hold(lua_State *state, dsl_pool_t *dp, const char *dsname,
       const void *tag)
   {
           dsl_dataset_t *ds;
           int error = dsl_dataset_hold(dp, dsname, tag, &ds);
           (void) zcp_dataset_hold_error(state, dp, dsname, error);
           return (ds);
   }
   
   static int zcp_debug(lua_State *);
   static const zcp_lib_info_t zcp_debug_info = {
           .name = "debug",
           .func = zcp_debug,
           .pargs = {
               { .za_name = "debug string", .za_lua_type = LUA_TSTRING },
               {NULL, 0}
           },
           .kwargs = {
               {NULL, 0}
           }
   };
   
   static int
   zcp_debug(lua_State *state)
   {
           const char *dbgstring;
           zcp_run_info_t *ri = zcp_run_info(state);
           const zcp_lib_info_t *libinfo = &zcp_debug_info;
   
           zcp_parse_args(state, libinfo->name, libinfo->pargs, libinfo->kwargs);
   
           dbgstring = lua_tostring(state, 1);
   
           zfs_dbgmsg("txg %lld ZCP: %s", (longlong_t)ri->zri_tx->tx_txg,
               dbgstring);
   
           return (0);
   }
   
   static int zcp_exists(lua_State *);
   static const zcp_lib_info_t zcp_exists_info = {
           .name = "exists",
           .func = zcp_exists,
           .pargs = {
               { .za_name = "dataset", .za_lua_type = LUA_TSTRING },
               {NULL, 0}
           },
           .kwargs = {
               {NULL, 0}
           }
   };
   
   static int
   zcp_exists(lua_State *state)
   {
           zcp_run_info_t *ri = zcp_run_info(state);
           dsl_pool_t *dp = ri->zri_pool;
           const zcp_lib_info_t *libinfo = &zcp_exists_info;
   
           zcp_parse_args(state, libinfo->name, libinfo->pargs, libinfo->kwargs);
   
           const char *dsname = lua_tostring(state, 1);
   
           dsl_dataset_t *ds;
           int error = dsl_dataset_hold(dp, dsname, FTAG, &ds);
           if (error == 0) {
                   dsl_dataset_rele(ds, FTAG);
                   lua_pushboolean(state, B_TRUE);
           } else if (error == ENOENT) {
                   lua_pushboolean(state, B_FALSE);
           } else if (error == EXDEV) {
                   return (luaL_error(state, "dataset '%s' is not in the "
                       "target pool", dsname));
           } else if (error == EIO) {
                   return (luaL_error(state, "I/O error opening dataset '%s'",
                       dsname));
           } else if (error != 0) {
                   return (luaL_error(state, "unexpected error %d", error));
           }
   
           return (1);
   }
   
   /*
    * Allocate/realloc/free a buffer for the lua interpreter.
    *
    * When nsize is 0, behaves as free() and returns NULL.
    *
    * If ptr is NULL, behaves as malloc() and returns an allocated buffer of size
    * at least nsize.
    *
    * Otherwise, behaves as realloc(), changing the allocation from osize to nsize.
    * Shrinking the buffer size never fails.
    *
    * The original allocated buffer size is stored as a uint64 at the beginning of
    * the buffer to avoid actually reallocating when shrinking a buffer, since lua
    * requires that this operation never fail.
    */
   static void *
   zcp_lua_alloc(void *ud, void *ptr, size_t osize, size_t nsize)
   {
           zcp_alloc_arg_t *allocargs = ud;
   
           if (nsize == 0) {
                   if (ptr != NULL) {
                           int64_t *allocbuf = (int64_t *)ptr - 1;
                           int64_t allocsize = *allocbuf;
                           ASSERT3S(allocsize, >, 0);
                           ASSERT3S(allocargs->aa_alloc_remaining + allocsize, <=,
                               allocargs->aa_alloc_limit);
                           allocargs->aa_alloc_remaining += allocsize;
                           vmem_free(allocbuf, allocsize);
                   }
                   return (NULL);
           } else if (ptr == NULL) {
                   int64_t *allocbuf;
                   int64_t allocsize = nsize + sizeof (int64_t);
   
                   if (!allocargs->aa_must_succeed &&
                       (allocsize <= 0 ||
                       allocsize > allocargs->aa_alloc_remaining)) {
                           return (NULL);
                   }
   
                   allocbuf = vmem_alloc(allocsize, KM_SLEEP);
                   allocargs->aa_alloc_remaining -= allocsize;
   
                   *allocbuf = allocsize;
                   return (allocbuf + 1);
           } else if (nsize <= osize) {
                   /*
                    * If shrinking the buffer, lua requires that the reallocation
                    * never fail.
                    */
                   return (ptr);
           } else {
                   ASSERT3U(nsize, >, osize);
   
                   uint64_t *luabuf = zcp_lua_alloc(ud, NULL, 0, nsize);
                   if (luabuf == NULL) {
                           return (NULL);
                   }
                   (void) memcpy(luabuf, ptr, osize);
                   VERIFY3P(zcp_lua_alloc(ud, ptr, osize, 0), ==, NULL);
                   return (luabuf);
           }
   }
   
   static void
   zcp_lua_counthook(lua_State *state, lua_Debug *ar)
   {
           (void) ar;
           lua_getfield(state, LUA_REGISTRYINDEX, ZCP_RUN_INFO_KEY);
           zcp_run_info_t *ri = lua_touserdata(state, -1);
   
           /*
            * Check if we were canceled while waiting for the
            * txg to sync or from our open context thread
            */
           if (ri->zri_canceled ||
               (!ri->zri_sync && issig(JUSTLOOKING) && issig(FORREAL))) {
                   ri->zri_canceled = B_TRUE;
                   (void) lua_pushstring(state, "Channel program was canceled.");
                   (void) lua_error(state);
                   /* Unreachable */
           }
   
           /*
            * Check how many instructions the channel program has
            * executed so far, and compare against the limit.
            */
           ri->zri_curinstrs += zfs_lua_check_instrlimit_interval;
           if (ri->zri_maxinstrs != 0 && ri->zri_curinstrs > ri->zri_maxinstrs) {
                   ri->zri_timed_out = B_TRUE;
                   (void) lua_pushstring(state,
                       "Channel program timed out.");
                   (void) lua_error(state);
                   /* Unreachable */
           }
   }
   
   static int
   zcp_panic_cb(lua_State *state)
   {
           panic("unprotected error in call to Lua API (%s)\n",
               lua_tostring(state, -1));
           return (0);
   }
   
   static void
   zcp_eval_impl(dmu_tx_t *tx, zcp_run_info_t *ri)
   {
           int err;
           lua_State *state = ri->zri_state;
   
           VERIFY3U(3, ==, lua_gettop(state));
   
           /* finish initializing our runtime state */
           ri->zri_pool = dmu_tx_pool(tx);
           ri->zri_tx = tx;
           list_create(&ri->zri_cleanup_handlers, sizeof (zcp_cleanup_handler_t),
               offsetof(zcp_cleanup_handler_t, zch_node));
   
           /*
            * Store the zcp_run_info_t struct for this run in the Lua registry.
            * Registry entries are not directly accessible by the Lua scripts but
            * can be accessed by our callbacks.
            */
           lua_pushlightuserdata(state, ri);
           lua_setfield(state, LUA_REGISTRYINDEX, ZCP_RUN_INFO_KEY);
           VERIFY3U(3, ==, lua_gettop(state));
   
           /*
            * Tell the Lua interpreter to call our handler every count
            * instructions. Channel programs that execute too many instructions
            * should die with ETIME.
            */
           (void) lua_sethook(state, zcp_lua_counthook, LUA_MASKCOUNT,
               zfs_lua_check_instrlimit_interval);
   
           /*
            * Tell the Lua memory allocator to stop using KM_SLEEP before handing
            * off control to the channel program. Channel programs that use too
            * much memory should die with ENOSPC.
            */
           ri->zri_allocargs->aa_must_succeed = B_FALSE;
   
           /*
            * Call the Lua function that open-context passed us. This pops the
            * function and its input from the stack and pushes any return
            * or error values.
            */
           err = lua_pcall(state, 1, LUA_MULTRET, 1);
   
           /*
            * Let Lua use KM_SLEEP while we interpret the return values.
            */
           ri->zri_allocargs->aa_must_succeed = B_TRUE;
   
           /*
            * Remove the error handler callback from the stack. At this point,
            * there shouldn't be any cleanup handler registered in the handler
            * list (zri_cleanup_handlers), regardless of whether it ran or not.
            */
           list_destroy(&ri->zri_cleanup_handlers);
           lua_remove(state, 1);
   
           switch (err) {
           case LUA_OK: {
                   /*
                    * Lua supports returning multiple values in a single return
                    * statement.  Return values will have been pushed onto the
                    * stack:
                    * 1: Return value 1
                    * 2: Return value 2
                    * 3: etc...
                    * To simplify the process of retrieving a return value from a
                    * channel program, we disallow returning more than one value
                    * to ZFS from the Lua script, yielding a singleton return
                    * nvlist of the form { "return": Return value 1 }.
                    */
                   int return_count = lua_gettop(state);
   
                   if (return_count == 1) {
                           ri->zri_result = 0;
                           zcp_convert_return_values(state, ri->zri_outnvl,
                               ZCP_RET_RETURN, &ri->zri_result);
                   } else if (return_count > 1) {
                           ri->zri_result = SET_ERROR(ECHRNG);
                           lua_settop(state, 0);
                           (void) lua_pushfstring(state, "Multiple return "
                               "values not supported");
                           zcp_convert_return_values(state, ri->zri_outnvl,
                               ZCP_RET_ERROR, &ri->zri_result);
                   }
                   break;
           }
           case LUA_ERRRUN:
           case LUA_ERRGCMM: {
                   /*
                    * The channel program encountered a fatal error within the
                    * script, such as failing an assertion, or calling a function
                    * with incompatible arguments. The error value and the
                    * traceback generated by zcp_error_handler() should be on the
                    * stack.
                    */
                   VERIFY3U(1, ==, lua_gettop(state));
                   if (ri->zri_timed_out) {
                           ri->zri_result = SET_ERROR(ETIME);
                   } else if (ri->zri_canceled) {
                           ri->zri_result = SET_ERROR(EINTR);
                   } else {
                           ri->zri_result = SET_ERROR(ECHRNG);
                   }
   
                   zcp_convert_return_values(state, ri->zri_outnvl,
                       ZCP_RET_ERROR, &ri->zri_result);
   
                   if (ri->zri_result == ETIME && ri->zri_outnvl != NULL) {
                           (void) nvlist_add_uint64(ri->zri_outnvl,
                               ZCP_ARG_INSTRLIMIT, ri->zri_curinstrs);
                   }
                   break;
           }
           case LUA_ERRERR: {
                   /*
                    * The channel program encountered a fatal error within the
                    * script, and we encountered another error while trying to
                    * compute the traceback in zcp_error_handler(). We can only
                    * return the error message.
                    */
                   VERIFY3U(1, ==, lua_gettop(state));
                   if (ri->zri_timed_out) {
                           ri->zri_result = SET_ERROR(ETIME);
                   } else if (ri->zri_canceled) {
                           ri->zri_result = SET_ERROR(EINTR);
                   } else {
                           ri->zri_result = SET_ERROR(ECHRNG);
                   }
   
                   zcp_convert_return_values(state, ri->zri_outnvl,
                       ZCP_RET_ERROR, &ri->zri_result);
                   break;
           }
           case LUA_ERRMEM:
                   /*
                    * Lua ran out of memory while running the channel program.
                    * There's not much we can do.
                    */
                   ri->zri_result = SET_ERROR(ENOSPC);
                   break;
           default:
                   VERIFY0(err);
           }
   }
   
   static void
   zcp_pool_error(zcp_run_info_t *ri, const char *poolname, int error)
   {
           ri->zri_result = SET_ERROR(ECHRNG);
           lua_settop(ri->zri_state, 0);
           (void) lua_pushfstring(ri->zri_state, "Could not open pool: %s "
               "errno: %d", poolname, error);
           zcp_convert_return_values(ri->zri_state, ri->zri_outnvl,
               ZCP_RET_ERROR, &ri->zri_result);
   
   }
   
   /*
    * This callback is called when txg_wait_synced_sig encountered a signal.
    * The txg_wait_synced_sig will continue to wait for the txg to complete
    * after calling this callback.
    */
   static void
   zcp_eval_sig(void *arg, dmu_tx_t *tx)
   {
           (void) tx;
           zcp_run_info_t *ri = arg;
   
           ri->zri_canceled = B_TRUE;
   }
   
   static void
   zcp_eval_sync(void *arg, dmu_tx_t *tx)
   {
           zcp_run_info_t *ri = arg;
   
           /*
            * Open context should have setup the stack to contain:
            * 1: Error handler callback
            * 2: Script to run (converted to a Lua function)
            * 3: nvlist input to function (converted to Lua table or nil)
            */
           VERIFY3U(3, ==, lua_gettop(ri->zri_state));
   
           zcp_eval_impl(tx, ri);
  }
  
  static void
  zcp_eval_open(zcp_run_info_t *ri, const char *poolname)
  {
          int error;
          dsl_pool_t *dp;
          dmu_tx_t *tx;
  
          /*
           * See comment from the same assertion in zcp_eval_sync().
           */
          VERIFY3U(3, ==, lua_gettop(ri->zri_state));
  
          error = dsl_pool_hold(poolname, FTAG, &dp);
          if (error != 0) {
                  zcp_pool_error(ri, poolname, error);
                  return;
          }
  
          /*
           * As we are running in open-context, we have no transaction associated
           * with the channel program. At the same time, functions from the
           * zfs.check submodule need to be associated with a transaction as
           * they are basically dry-runs of their counterparts in the zfs.sync
           * submodule. These functions should be able to run in open-context.
           * Therefore we create a new transaction that we later abort once
           * the channel program has been evaluated.
           */
          tx = dmu_tx_create_dd(dp->dp_mos_dir);
  
          zcp_eval_impl(tx, ri);
  
          dmu_tx_abort(tx);
  
          dsl_pool_rele(dp, FTAG);
  }
  
  int
  zcp_eval(const char *poolname, const char *program, boolean_t sync,
      uint64_t instrlimit, uint64_t memlimit, nvpair_t *nvarg, nvlist_t *outnvl)
  {
          int err;
          lua_State *state;
          zcp_run_info_t runinfo;
  
          if (instrlimit > zfs_lua_max_instrlimit)
                  return (SET_ERROR(EINVAL));
          if (memlimit == 0 || memlimit > zfs_lua_max_memlimit)
                  return (SET_ERROR(EINVAL));
  
          zcp_alloc_arg_t allocargs = {
                  .aa_must_succeed = B_TRUE,
                  .aa_alloc_remaining = (int64_t)memlimit,
                  .aa_alloc_limit = (int64_t)memlimit,
          };
  
          /*
           * Creates a Lua state with a memory allocator that uses KM_SLEEP.
           * This should never fail.
           */
          state = lua_newstate(zcp_lua_alloc, &allocargs);
          VERIFY(state != NULL);
          (void) lua_atpanic(state, zcp_panic_cb);
  
          /*
           * Load core Lua libraries we want access to.
           */
          VERIFY3U(1, ==, luaopen_base(state));
          lua_pop(state, 1);
          VERIFY3U(1, ==, luaopen_coroutine(state));
          lua_setglobal(state, LUA_COLIBNAME);
          VERIFY0(lua_gettop(state));
          VERIFY3U(1, ==, luaopen_string(state));
          lua_setglobal(state, LUA_STRLIBNAME);
          VERIFY0(lua_gettop(state));
          VERIFY3U(1, ==, luaopen_table(state));
          lua_setglobal(state, LUA_TABLIBNAME);
          VERIFY0(lua_gettop(state));
  
          /*
           * Load globally visible variables such as errno aliases.
           */
          zcp_load_globals(state);
          VERIFY0(lua_gettop(state));
  
          /*
           * Load ZFS-specific modules.
           */
          lua_newtable(state);
          VERIFY3U(1, ==, zcp_load_list_lib(state));
          lua_setfield(state, -2, "list");
          VERIFY3U(1, ==, zcp_load_synctask_lib(state, B_FALSE));
          lua_setfield(state, -2, "check");
          VERIFY3U(1, ==, zcp_load_synctask_lib(state, B_TRUE));
          lua_setfield(state, -2, "sync");
          VERIFY3U(1, ==, zcp_load_get_lib(state));
          lua_pushcclosure(state, zcp_debug_info.func, 0);
          lua_setfield(state, -2, zcp_debug_info.name);
          lua_pushcclosure(state, zcp_exists_info.func, 0);
          lua_setfield(state, -2, zcp_exists_info.name);
          lua_setglobal(state, "zfs");
          VERIFY0(lua_gettop(state));
  
          /*
           * Push the error-callback that calculates Lua stack traces on
           * unexpected failures.
           */
          lua_pushcfunction(state, zcp_error_handler);
          VERIFY3U(1, ==, lua_gettop(state));
  
          /*
           * Load the actual script as a function onto the stack as text ("t").
           * The only valid error condition is a syntax error in the script.
           * ERRMEM should not be possible because our allocator is using
           * KM_SLEEP.  ERRGCMM should not be possible because we have not added
           * any objects with __gc metamethods to the interpreter that could
           * fail.
           */
          err = luaL_loadbufferx(state, program, strlen(program),
              "channel program", "t");
          if (err == LUA_ERRSYNTAX) {
                  fnvlist_add_string(outnvl, ZCP_RET_ERROR,
                      lua_tostring(state, -1));
                  lua_close(state);
                  return (SET_ERROR(EINVAL));
          }
          VERIFY0(err);
          VERIFY3U(2, ==, lua_gettop(state));
  
          /*
           * Convert the input nvlist to a Lua object and put it on top of the
           * stack.
           */
          char errmsg[128];
          err = zcp_nvpair_value_to_lua(state, nvarg,
              errmsg, sizeof (errmsg));
          if (err != 0) {
                  fnvlist_add_string(outnvl, ZCP_RET_ERROR, errmsg);
                  lua_close(state);
                  return (SET_ERROR(EINVAL));
          }
          VERIFY3U(3, ==, lua_gettop(state));
  
          runinfo.zri_state = state;
          runinfo.zri_allocargs = &allocargs;
          runinfo.zri_outnvl = outnvl;
          runinfo.zri_result = 0;
          runinfo.zri_cred = CRED();
          runinfo.zri_proc = curproc;
          runinfo.zri_timed_out = B_FALSE;
          runinfo.zri_canceled = B_FALSE;
          runinfo.zri_sync = sync;
          runinfo.zri_space_used = 0;
          runinfo.zri_curinstrs = 0;
          runinfo.zri_maxinstrs = instrlimit;
          runinfo.zri_new_zvols = fnvlist_alloc();
  
          if (sync) {
                  err = dsl_sync_task_sig(poolname, NULL, zcp_eval_sync,
                      zcp_eval_sig, &runinfo, 0, ZFS_SPACE_CHECK_ZCP_EVAL);
                  if (err != 0)
                          zcp_pool_error(&runinfo, poolname, err);
          } else {
                  zcp_eval_open(&runinfo, poolname);
          }
          lua_close(state);
  
          /*
           * Create device minor nodes for any new zvols.
           */
          for (nvpair_t *pair = nvlist_next_nvpair(runinfo.zri_new_zvols, NULL);
              pair != NULL;
              pair = nvlist_next_nvpair(runinfo.zri_new_zvols, pair)) {
                  zvol_create_minor(nvpair_name(pair));
          }
          fnvlist_free(runinfo.zri_new_zvols);
  
          return (runinfo.zri_result);
  }
  
  /*
   * Retrieve metadata about the currently running channel program.
   */
  zcp_run_info_t *
  zcp_run_info(lua_State *state)
  {
          zcp_run_info_t *ri;
  
          lua_getfield(state, LUA_REGISTRYINDEX, ZCP_RUN_INFO_KEY);
          ri = lua_touserdata(state, -1);
          lua_pop(state, 1);
          return (ri);
  }
  
  /*
   * Argument Parsing
   * ================
   *
   * The Lua language allows methods to be called with any number
   * of arguments of any type. When calling back into ZFS we need to sanitize
   * arguments from channel programs to make sure unexpected arguments or
   * arguments of the wrong type result in clear error messages. To do this
   * in a uniform way all callbacks from channel programs should use the
   * zcp_parse_args() function to interpret inputs.
   *
   * Positional vs Keyword Arguments
   * ===============================
   *
   * Every callback function takes a fixed set of required positional arguments
   * and optional keyword arguments. For example, the destroy function takes
   * a single positional string argument (the name of the dataset to destroy)
   * and an optional "defer" keyword boolean argument. When calling lua functions
   * with parentheses, only positional arguments can be used:
   *
   *     zfs.sync.snapshot("rpool@snap")
   *
   * To use keyword arguments functions should be called with a single argument
   * that is a lua table containing mappings of integer -> positional arguments
   * and string -> keyword arguments:
   *
   *     zfs.sync.snapshot({1="rpool@snap", defer=true})
   *
   * The lua language allows curly braces to be used in place of parenthesis as
   * syntactic sugar for this calling convention:
   *
   *     zfs.sync.snapshot{"rpool@snap", defer=true}
   */
  
  /*
   * Throw an error and print the given arguments.  If there are too many
   * arguments to fit in the output buffer, only the error format string is
   * output.
   */
  static void
  zcp_args_error(lua_State *state, const char *fname, const zcp_arg_t *pargs,
      const zcp_arg_t *kwargs, const char *fmt, ...)
  {
          int i;
          char errmsg[512];
          size_t len = sizeof (errmsg);
          size_t msglen = 0;
          va_list argp;
  
          va_start(argp, fmt);
          VERIFY3U(len, >, vsnprintf(errmsg, len, fmt, argp));
          va_end(argp);
  
          /*
           * Calculate the total length of the final string, including extra
           * formatting characters. If the argument dump would be too large,
           * only print the error string.
           */
          msglen = strlen(errmsg);
          msglen += strlen(fname) + 4; /* : + {} + null terminator */
          for (i = 0; pargs[i].za_name != NULL; i++) {
                  msglen += strlen(pargs[i].za_name);
                  msglen += strlen(lua_typename(state, pargs[i].za_lua_type));
                  if (pargs[i + 1].za_name != NULL || kwargs[0].za_name != NULL)
                          msglen += 5; /* < + ( + )> + , */
                  else
                          msglen += 4; /* < + ( + )> */
          }
          for (i = 0; kwargs[i].za_name != NULL; i++) {
                  msglen += strlen(kwargs[i].za_name);
                  msglen += strlen(lua_typename(state, kwargs[i].za_lua_type));
                  if (kwargs[i + 1].za_name != NULL)
                          msglen += 4; /* =( + ) + , */
                  else
                          msglen += 3; /* =( + ) */
          }
  
          if (msglen >= len)
                  (void) luaL_error(state, errmsg);
  
          VERIFY3U(len, >, strlcat(errmsg, ": ", len));
          VERIFY3U(len, >, strlcat(errmsg, fname, len));
          VERIFY3U(len, >, strlcat(errmsg, "{", len));
          for (i = 0; pargs[i].za_name != NULL; i++) {
                  VERIFY3U(len, >, strlcat(errmsg, "<", len));
                  VERIFY3U(len, >, strlcat(errmsg, pargs[i].za_name, len));
                  VERIFY3U(len, >, strlcat(errmsg, "(", len));
                  VERIFY3U(len, >, strlcat(errmsg,
                      lua_typename(state, pargs[i].za_lua_type), len));
                  VERIFY3U(len, >, strlcat(errmsg, ")>", len));
                  if (pargs[i + 1].za_name != NULL || kwargs[0].za_name != NULL) {
                          VERIFY3U(len, >, strlcat(errmsg, ", ", len));
                  }
          }
          for (i = 0; kwargs[i].za_name != NULL; i++) {
                  VERIFY3U(len, >, strlcat(errmsg, kwargs[i].za_name, len));
                  VERIFY3U(len, >, strlcat(errmsg, "=(", len));
                  VERIFY3U(len, >, strlcat(errmsg,
                      lua_typename(state, kwargs[i].za_lua_type), len));
                  VERIFY3U(len, >, strlcat(errmsg, ")", len));
                  if (kwargs[i + 1].za_name != NULL) {
                          VERIFY3U(len, >, strlcat(errmsg, ", ", len));
                  }
          }
          VERIFY3U(len, >, strlcat(errmsg, "}", len));
  
          (void) luaL_error(state, errmsg);
          panic("unreachable code");
  }
  
  static void
  zcp_parse_table_args(lua_State *state, const char *fname,
      const zcp_arg_t *pargs, const zcp_arg_t *kwargs)
  {
          int i;
          int type;
  
          for (i = 0; pargs[i].za_name != NULL; i++) {
                  /*
                   * Check the table for this positional argument, leaving it
                   * on the top of the stack once we finish validating it.
                   */
                  lua_pushinteger(state, i + 1);
                  lua_gettable(state, 1);
  
                  type = lua_type(state, -1);
                  if (type == LUA_TNIL) {
                          zcp_args_error(state, fname, pargs, kwargs,
                              "too few arguments");
                          panic("unreachable code");
                  } else if (type != pargs[i].za_lua_type) {
                          zcp_args_error(state, fname, pargs, kwargs,
                              "arg %d wrong type (is '%s', expected '%s')",
                              i + 1, lua_typename(state, type),
                              lua_typename(state, pargs[i].za_lua_type));
                          panic("unreachable code");
                  }
  
                  /*
                   * Remove the positional argument from the table.
                   */
                  lua_pushinteger(state, i + 1);
                  lua_pushnil(state);
                  lua_settable(state, 1);
          }
  
          for (i = 0; kwargs[i].za_name != NULL; i++) {
                  /*
                   * Check the table for this keyword argument, which may be
                   * nil if it was omitted. Leave the value on the top of
                   * the stack after validating it.
                   */
                  lua_getfield(state, 1, kwargs[i].za_name);
  
                  type = lua_type(state, -1);
                  if (type != LUA_TNIL && type != kwargs[i].za_lua_type) {
                          zcp_args_error(state, fname, pargs, kwargs,
                              "kwarg '%s' wrong type (is '%s', expected '%s')",
                              kwargs[i].za_name, lua_typename(state, type),
                              lua_typename(state, kwargs[i].za_lua_type));
                          panic("unreachable code");
                  }
  
                  /*
                   * Remove the keyword argument from the table.
                   */
                  lua_pushnil(state);
                  lua_setfield(state, 1, kwargs[i].za_name);
          }
  
          /*
           * Any entries remaining in the table are invalid inputs, print
           * an error message based on what the entry is.
           */
          lua_pushnil(state);
          if (lua_next(state, 1)) {
                  if (lua_isnumber(state, -2) && lua_tointeger(state, -2) > 0) {
                          zcp_args_error(state, fname, pargs, kwargs,
                              "too many positional arguments");
                  } else if (lua_isstring(state, -2)) {
                          zcp_args_error(state, fname, pargs, kwargs,
                              "invalid kwarg '%s'", lua_tostring(state, -2));
                  } else {
                          zcp_args_error(state, fname, pargs, kwargs,
                              "kwarg keys must be strings");
                  }
                  panic("unreachable code");
          }
  
          lua_remove(state, 1);
  }
  
  static void
  zcp_parse_pos_args(lua_State *state, const char *fname, const zcp_arg_t *pargs,
      const zcp_arg_t *kwargs)
  {
          int i;
          int type;
  
          for (i = 0; pargs[i].za_name != NULL; i++) {
                  type = lua_type(state, i + 1);
                  if (type == LUA_TNONE) {
                          zcp_args_error(state, fname, pargs, kwargs,
                              "too few arguments");
                          panic("unreachable code");
                  } else if (type != pargs[i].za_lua_type) {
                          zcp_args_error(state, fname, pargs, kwargs,
                              "arg %d wrong type (is '%s', expected '%s')",
                              i + 1, lua_typename(state, type),
                              lua_typename(state, pargs[i].za_lua_type));
                          panic("unreachable code");
                  }
          }
          if (lua_gettop(state) != i) {
                  zcp_args_error(state, fname, pargs, kwargs,
                      "too many positional arguments");
                  panic("unreachable code");
          }
  
          for (i = 0; kwargs[i].za_name != NULL; i++) {
                  lua_pushnil(state);
          }
  }
  
  /*
   * Checks the current Lua stack against an expected set of positional and
   * keyword arguments. If the stack does not match the expected arguments
   * aborts the current channel program with a useful error message, otherwise
   * it re-arranges the stack so that it contains the positional arguments
   * followed by the keyword argument values in declaration order. Any missing
   * keyword argument will be represented by a nil value on the stack.
   *
   * If the stack contains exactly one argument of type LUA_TTABLE the curly
   * braces calling convention is assumed, otherwise the stack is parsed for
   * positional arguments only.
   *
   * This function should be used by every function callback. It should be called
   * before the callback manipulates the Lua stack as it assumes the stack
   * represents the function arguments.
   */
  void
  zcp_parse_args(lua_State *state, const char *fname, const zcp_arg_t *pargs,
      const zcp_arg_t *kwargs)
  {
          if (lua_gettop(state) == 1 && lua_istable(state, 1)) {
                  zcp_parse_table_args(state, fname, pargs, kwargs);
          } else {
                  zcp_parse_pos_args(state, fname, pargs, kwargs);
          }
  }
  
  ZFS_MODULE_PARAM(zfs_lua, zfs_lua_, max_instrlimit, U64, ZMOD_RW,
          "Max instruction limit that can be specified for a channel program");
  
  ZFS_MODULE_PARAM(zfs_lua, zfs_lua_, max_memlimit, U64, ZMOD_RW,
          "Max memory limit that can be specified for a channel program");

Cache object: 338033f7ae284a8b025174f50847ccb4