FreeBSD/Linux Kernel Cross Reference
sys/fs/nfs/write.c

     /*
      * linux/fs/nfs/write.c
      *
      * Writing file data over NFS.
      *
      * We do it like this: When a (user) process wishes to write data to an
      * NFS file, a write request is allocated that contains the RPC task data
      * plus some info on the page to be written, and added to the inode's
      * write chain. If the process writes past the end of the page, an async
     * RPC call to write the page is scheduled immediately; otherwise, the call
     * is delayed for a few seconds.
     *
     * Just like readahead, no async I/O is performed if wsize < PAGE_SIZE.
     *
     * Write requests are kept on the inode's writeback list. Each entry in
     * that list references the page (portion) to be written. When the
     * cache timeout has expired, the RPC task is woken up, and tries to
     * lock the page. As soon as it manages to do so, the request is moved
     * from the writeback list to the writelock list.
     *
     * Note: we must make sure never to confuse the inode passed in the
     * write_page request with the one in page->inode. As far as I understand
     * it, these are different when doing a swap-out.
     *
     * To understand everything that goes on here and in the NFS read code,
     * one should be aware that a page is locked in exactly one of the following
     * cases:
     *
     *  -   A write request is in progress.
     *  -   A user process is in generic_file_write/nfs_update_page
     *  -   A user process is in generic_file_read
     *
     * Also note that because of the way pages are invalidated in
     * nfs_revalidate_inode, the following assertions hold:
     *
     *  -   If a page is dirty, there will be no read requests (a page will
     *      not be re-read unless invalidated by nfs_revalidate_inode).
     *  -   If the page is not uptodate, there will be no pending write
     *      requests, and no process will be in nfs_update_page.
     *
     * FIXME: Interaction with the vmscan routines is not optimal yet.
     * Either vmscan must be made nfs-savvy, or we need a different page
     * reclaim concept that supports something like FS-independent
     * buffer_heads with a b_ops-> field.
     *
     * Copyright (C) 1996, 1997, Olaf Kirch <okir@monad.swb.de>
     */
    
    #include <linux/config.h>
    #include <linux/types.h>
    #include <linux/slab.h>
    #include <linux/swap.h>
    #include <linux/pagemap.h>
    #include <linux/file.h>
    
    #include <linux/sunrpc/clnt.h>
    #include <linux/nfs_fs.h>
    #include <linux/nfs_mount.h>
    #include <linux/nfs_flushd.h>
    #include <linux/nfs_page.h>
    #include <asm/uaccess.h>
    #include <linux/smp_lock.h>
    
    #define NFSDBG_FACILITY         NFSDBG_PAGECACHE
    
    /*
     * Local structures
     *
     * This is the struct where the WRITE/COMMIT arguments go.
     */
    struct nfs_write_data {
            struct rpc_task         task;
            struct inode            *inode;
            struct rpc_cred         *cred;
            struct nfs_writeargs    args;           /* argument struct */
            struct nfs_writeres     res;            /* result struct */
            struct nfs_fattr        fattr;
            struct nfs_writeverf    verf;
            struct list_head        pages;          /* Coalesced requests we wish to flush */
            struct page             *pagevec[NFS_WRITE_MAXIOV];
    };
    
    /*
     * Local function declarations
     */
    static struct nfs_page * nfs_update_request(struct file*, struct inode *,
                                                struct page *,
                                                unsigned int, unsigned int);
    static void     nfs_strategy(struct inode *inode);
    static void     nfs_writeback_done(struct rpc_task *);
    #ifdef CONFIG_NFS_V3
    static void     nfs_commit_done(struct rpc_task *);
    #endif
    
    /* Hack for future NFS swap support */
    #ifndef IS_SWAPFILE
    # define IS_SWAPFILE(inode)     (0)
    #endif
    
   static kmem_cache_t *nfs_wdata_cachep;
   
   static __inline__ struct nfs_write_data *nfs_writedata_alloc(void)
   {
           struct nfs_write_data   *p;
           p = kmem_cache_alloc(nfs_wdata_cachep, SLAB_NOFS);
           if (p) {
                   memset(p, 0, sizeof(*p));
                   INIT_LIST_HEAD(&p->pages);
                   p->args.pages = p->pagevec;
           }
           return p;
   }
   
   static __inline__ void nfs_writedata_free(struct nfs_write_data *p)
   {
           kmem_cache_free(nfs_wdata_cachep, p);
   }
   
   static void nfs_writedata_release(struct rpc_task *task)
   {
           struct nfs_write_data   *wdata = (struct nfs_write_data *)task->tk_calldata;
           nfs_writedata_free(wdata);
   }
   
   /*
    * Write a page synchronously.
    * Offset is the data offset within the page.
    */
   static int
   nfs_writepage_sync(struct file *file, struct inode *inode, struct page *page,
                      unsigned int offset, unsigned int count)
   {
           struct rpc_cred *cred = NULL;
           loff_t          base;
           unsigned int    wsize = NFS_SERVER(inode)->wsize;
           int             result, refresh = 0, written = 0, flags;
           u8              *buffer;
           struct nfs_fattr fattr;
           struct nfs_writeverf verf;
   
   
           if (file)
                   cred = get_rpccred(nfs_file_cred(file));
           if (!cred)
                   cred = get_rpccred(NFS_I(inode)->mm_cred);
   
           dprintk("NFS:      nfs_writepage_sync(%x/%Ld %d@%Ld)\n",
                   inode->i_dev, (long long)NFS_FILEID(inode),
                   count, (long long)(page_offset(page) + offset));
   
           base = page_offset(page) + offset;
   
           flags = ((IS_SWAPFILE(inode)) ? NFS_RW_SWAP : 0) | NFS_RW_SYNC;
   
           do {
                   if (count < wsize && !IS_SWAPFILE(inode))
                           wsize = count;
   
                   result = NFS_PROTO(inode)->write(inode, cred, &fattr, flags,
                                                    offset, wsize, page, &verf);
                   nfs_write_attributes(inode, &fattr);
   
                   if (result < 0) {
                           /* Must mark the page invalid after I/O error */
                           ClearPageUptodate(page);
                           goto io_error;
                   }
                   if (result != wsize)
                           printk("NFS: short write, wsize=%u, result=%d\n",
                           wsize, result);
                   refresh = 1;
                   buffer  += wsize;
                   base    += wsize;
                   offset  += wsize;
                   written += wsize;
                   count   -= wsize;
                   /*
                    * If we've extended the file, update the inode
                    * now so we don't invalidate the cache.
                    */
                   if (base > inode->i_size)
                           inode->i_size = base;
           } while (count);
   
           if (PageError(page))
                   ClearPageError(page);
   
   io_error:
           if (cred)
                   put_rpccred(cred);
   
           return written? written : result;
   }
   
   static int
   nfs_writepage_async(struct file *file, struct inode *inode, struct page *page,
                       unsigned int offset, unsigned int count)
   {
           struct nfs_page *req;
           loff_t          end;
           int             status;
   
           req = nfs_update_request(file, inode, page, offset, count);
           status = (IS_ERR(req)) ? PTR_ERR(req) : 0;
           if (status < 0)
                   goto out;
           if (!req->wb_cred)
                   req->wb_cred = get_rpccred(NFS_I(inode)->mm_cred);
           nfs_unlock_request(req);
           nfs_strategy(inode);
           end = ((loff_t)page->index<<PAGE_CACHE_SHIFT) + (loff_t)(offset + count);
           if (inode->i_size < end)
                   inode->i_size = end;
   
    out:
           return status;
   }
   
   /*
    * Write an mmapped page to the server.
    */
   int
   nfs_writepage(struct page *page)
   {
           struct inode *inode = page->mapping->host;
           unsigned long end_index;
           unsigned offset = PAGE_CACHE_SIZE;
           int err;
   
           end_index = inode->i_size >> PAGE_CACHE_SHIFT;
   
           /* Ensure we've flushed out any previous writes */
           nfs_wb_page(inode,page);
   
           /* easy case */
           if (page->index < end_index)
                   goto do_it;
           /* things got complicated... */
           offset = inode->i_size & (PAGE_CACHE_SIZE-1);
   
           /* OK, are we completely out? */
           err = -EIO;
           if (page->index >= end_index+1 || !offset)
                   goto out;
   do_it:
           lock_kernel();
           if (NFS_SERVER(inode)->wsize >= PAGE_CACHE_SIZE && !IS_SYNC(inode)) {
                   err = nfs_writepage_async(NULL, inode, page, 0, offset);
                   if (err >= 0)
                           err = 0;
           } else {
                   err = nfs_writepage_sync(NULL, inode, page, 0, offset); 
                   if (err == offset)
                           err = 0;
           }
           unlock_kernel();
   out:
           UnlockPage(page);
           return err; 
   }
   
   /*
    * Check whether the file range we want to write to is locked by
    * us.
    */
   static int
   region_locked(struct inode *inode, struct nfs_page *req)
   {
           struct file_lock        *fl;
           loff_t                  rqstart, rqend;
   
           /* Don't optimize writes if we don't use NLM */
           if (NFS_SERVER(inode)->flags & NFS_MOUNT_NONLM)
                   return 0;
   
           rqstart = page_offset(req->wb_page) + req->wb_offset;
           rqend = rqstart + req->wb_bytes;
           for (fl = inode->i_flock; fl; fl = fl->fl_next) {
                   if (fl->fl_owner == current->files && (fl->fl_flags & FL_POSIX)
                       && fl->fl_type == F_WRLCK
                       && fl->fl_start <= rqstart && rqend <= fl->fl_end) {
                           return 1;
                   }
           }
   
           return 0;
   }
   
   /*
    * Insert a write request into an inode
    * Note: we sort the list in order to be able to optimize nfs_find_request()
    *       & co. for the 'write append' case. For 2.5 we may want to consider
    *       some form of hashing so as to perform well on random writes.
    */
   static inline void
   nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
   {
           struct list_head *pos, *head;
           unsigned long pg_idx = page_index(req->wb_page);
   
           if (!list_empty(&req->wb_hash))
                   return;
           if (!NFS_WBACK_BUSY(req))
                   printk(KERN_ERR "NFS: unlocked request attempted hashed!\n");
           head = &inode->u.nfs_i.writeback;
           if (list_empty(head))
                   igrab(inode);
           list_for_each_prev(pos, head) {
                   struct nfs_page *entry = nfs_inode_wb_entry(pos);
                   if (page_index(entry->wb_page) < pg_idx)
                           break;
           }
           inode->u.nfs_i.npages++;
           list_add(&req->wb_hash, pos);
           req->wb_count++;
   }
   
   /*
    * Insert a write request into an inode
    */
   static inline void
   nfs_inode_remove_request(struct nfs_page *req)
   {
           struct inode *inode;
           spin_lock(&nfs_wreq_lock);
           if (list_empty(&req->wb_hash)) {
                   spin_unlock(&nfs_wreq_lock);
                   return;
           }
           if (!NFS_WBACK_BUSY(req))
                   printk(KERN_ERR "NFS: unlocked request attempted unhashed!\n");
           inode = req->wb_inode;
           list_del(&req->wb_hash);
           INIT_LIST_HEAD(&req->wb_hash);
           inode->u.nfs_i.npages--;
           if ((inode->u.nfs_i.npages == 0) != list_empty(&inode->u.nfs_i.writeback))
                   printk(KERN_ERR "NFS: desynchronized value of nfs_i.npages.\n");
           if (list_empty(&inode->u.nfs_i.writeback)) {
                   spin_unlock(&nfs_wreq_lock);
                   iput(inode);
           } else
                   spin_unlock(&nfs_wreq_lock);
           nfs_clear_request(req);
           nfs_release_request(req);
   }
   
   /*
    * Find a request
    */
   static inline struct nfs_page *
   _nfs_find_request(struct inode *inode, struct page *page)
   {
           struct list_head        *head, *pos;
           unsigned long pg_idx = page_index(page);
   
           head = &inode->u.nfs_i.writeback;
           list_for_each_prev(pos, head) {
                   struct nfs_page *req = nfs_inode_wb_entry(pos);
                   unsigned long found_idx = page_index(req->wb_page);
   
                   if (pg_idx < found_idx)
                           continue;
                   if (pg_idx != found_idx)
                           break;
                   req->wb_count++;
                   return req;
           }
           return NULL;
   }
   
   static struct nfs_page *
   nfs_find_request(struct inode *inode, struct page *page)
   {
           struct nfs_page         *req;
   
           spin_lock(&nfs_wreq_lock);
           req = _nfs_find_request(inode, page);
           spin_unlock(&nfs_wreq_lock);
           return req;
   }
   
   /*
    * Add a request to the inode's dirty list.
    */
   static inline void
   nfs_mark_request_dirty(struct nfs_page *req)
   {
           struct inode *inode = req->wb_inode;
   
           spin_lock(&nfs_wreq_lock);
           nfs_list_add_request(req, &inode->u.nfs_i.dirty);
           inode->u.nfs_i.ndirty++;
           __nfs_del_lru(req);
           __nfs_add_lru(&NFS_SERVER(inode)->lru_dirty, req);
           spin_unlock(&nfs_wreq_lock);
           mark_inode_dirty(inode);
   }
   
   /*
    * Check if a request is dirty
    */
   static inline int
   nfs_dirty_request(struct nfs_page *req)
   {
           struct inode *inode = req->wb_inode;
           return !list_empty(&req->wb_list) && req->wb_list_head == &inode->u.nfs_i.dirty;
   }
   
   #ifdef CONFIG_NFS_V3
   /*
    * Add a request to the inode's commit list.
    */
   static inline void
   nfs_mark_request_commit(struct nfs_page *req)
   {
           struct inode *inode = req->wb_inode;
   
           spin_lock(&nfs_wreq_lock);
           nfs_list_add_request(req, &inode->u.nfs_i.commit);
           inode->u.nfs_i.ncommit++;
           __nfs_del_lru(req);
           __nfs_add_lru(&NFS_SERVER(inode)->lru_commit, req);
           spin_unlock(&nfs_wreq_lock);
           mark_inode_dirty(inode);
   }
   #endif
   
   /*
    * Wait for a request to complete.
    *
    * Interruptible by signals only if mounted with intr flag.
    */
   static int
   nfs_wait_on_requests(struct inode *inode, struct file *file, unsigned long idx_start, unsigned int npages)
   {
           struct list_head        *p, *head;
           unsigned long           idx_end;
           unsigned int            res = 0;
           int                     error;
   
           if (npages == 0)
                   idx_end = ~0;
           else
                   idx_end = idx_start + npages - 1;
   
           head = &inode->u.nfs_i.writeback;
    restart:
           spin_lock(&nfs_wreq_lock);
           list_for_each_prev(p, head) {
                   unsigned long pg_idx;
                   struct nfs_page *req = nfs_inode_wb_entry(p);
   
                   if (file && req->wb_file != file)
                           continue;
   
                   pg_idx = page_index(req->wb_page);
                   if (pg_idx < idx_start)
                           break;
                   if (pg_idx > idx_end)
                           continue;
   
                   if (!NFS_WBACK_BUSY(req))
                           continue;
                   req->wb_count++;
                   spin_unlock(&nfs_wreq_lock);
                   error = nfs_wait_on_request(req);
                   nfs_release_request(req);
                   if (error < 0)
                           return error;
                   res++;
                   goto restart;
           }
           spin_unlock(&nfs_wreq_lock);
           return res;
   }
   
   /**
    * nfs_scan_lru_dirty_timeout - Scan LRU list for timed out dirty requests
    * @server: NFS superblock data
    * @dst: destination list
    *
    * Moves a maximum of 'wpages' requests from the NFS dirty page LRU list.
    * The elements are checked to ensure that they form a contiguous set
    * of pages, and that they originated from the same file.
    */
   int
   nfs_scan_lru_dirty_timeout(struct nfs_server *server, struct list_head *dst)
   {
           struct inode *inode;
           int npages;
   
           npages = nfs_scan_lru_timeout(&server->lru_dirty, dst, server->wpages);
           if (npages) {
                   inode = nfs_list_entry(dst->next)->wb_inode;
                   inode->u.nfs_i.ndirty -= npages;
           }
           return npages;
   }
   
   /**
    * nfs_scan_lru_dirty - Scan LRU list for dirty requests
    * @server: NFS superblock data
    * @dst: destination list
    *
    * Moves a maximum of 'wpages' requests from the NFS dirty page LRU list.
    * The elements are checked to ensure that they form a contiguous set
    * of pages, and that they originated from the same file.
    */
   int
   nfs_scan_lru_dirty(struct nfs_server *server, struct list_head *dst)
   {
           struct inode *inode;
           int npages;
   
           npages = nfs_scan_lru(&server->lru_dirty, dst, server->wpages);
           if (npages) {
                   inode = nfs_list_entry(dst->next)->wb_inode;
                   inode->u.nfs_i.ndirty -= npages;
           }
           return npages;
   }
   
   /*
    * nfs_scan_dirty - Scan an inode for dirty requests
    * @inode: NFS inode to scan
    * @dst: destination list
    * @file: if set, ensure we match requests from this file
    * @idx_start: lower bound of page->index to scan.
    * @npages: idx_start + npages sets the upper bound to scan.
    *
    * Moves requests from the inode's dirty page list.
    * The requests are *not* checked to ensure that they form a contiguous set.
    */
   static int
   nfs_scan_dirty(struct inode *inode, struct list_head *dst, struct file *file, unsigned long idx_start, unsigned int npages)
   {
           int     res;
           res = nfs_scan_list(&inode->u.nfs_i.dirty, dst, file, idx_start, npages);
           inode->u.nfs_i.ndirty -= res;
           if ((inode->u.nfs_i.ndirty == 0) != list_empty(&inode->u.nfs_i.dirty))
                   printk(KERN_ERR "NFS: desynchronized value of nfs_i.ndirty.\n");
           return res;
   }
   
   #ifdef CONFIG_NFS_V3
   /**
    * nfs_scan_lru_commit_timeout - Scan LRU list for timed out commit requests
    * @server: NFS superblock data
    * @dst: destination list
    *
    * Finds the first a timed out request in the NFS commit LRU list and moves it
    * to the list dst. If such an element is found, we move all other commit
    * requests that apply to the same inode.
    * The assumption is that doing everything in a single commit-to-disk is
    * the cheaper alternative.
    */
   int
   nfs_scan_lru_commit_timeout(struct nfs_server *server, struct list_head *dst)
   {
           struct inode *inode;
           int npages;
   
           npages = nfs_scan_lru_timeout(&server->lru_commit, dst, 1);
           if (npages) {
                   inode = nfs_list_entry(dst->next)->wb_inode;
                   npages += nfs_scan_list(&inode->u.nfs_i.commit, dst, NULL, 0, 0);
                   inode->u.nfs_i.ncommit -= npages;
           }
           return npages;
   }
   
   
   /**
    * nfs_scan_lru_commit_timeout - Scan LRU list for timed out commit requests
    * @server: NFS superblock data
    * @dst: destination list
    *
    * Finds the first request in the NFS commit LRU list and moves it
    * to the list dst. If such an element is found, we move all other commit
    * requests that apply to the same inode.
    * The assumption is that doing everything in a single commit-to-disk is
    * the cheaper alternative.
    */
   int
   nfs_scan_lru_commit(struct nfs_server *server, struct list_head *dst)
   {
           struct inode *inode;
           int npages;
   
           npages = nfs_scan_lru(&server->lru_commit, dst, 1);
           if (npages) {
                   inode = nfs_list_entry(dst->next)->wb_inode;
                   npages += nfs_scan_list(&inode->u.nfs_i.commit, dst, NULL, 0, 0);
                   inode->u.nfs_i.ncommit -= npages;
           }
           return npages;
   }
   
   /*
    * nfs_scan_commit - Scan an inode for commit requests
    * @inode: NFS inode to scan
    * @dst: destination list
    * @file: if set, ensure we collect requests from this file only.
    * @idx_start: lower bound of page->index to scan.
    * @npages: idx_start + npages sets the upper bound to scan.
    *
    * Moves requests from the inode's 'commit' request list.
    * The requests are *not* checked to ensure that they form a contiguous set.
    */
   static int
   nfs_scan_commit(struct inode *inode, struct list_head *dst, struct file *file, unsigned long idx_start, unsigned int npages)
   {
           int     res;
           res = nfs_scan_list(&inode->u.nfs_i.commit, dst, file, idx_start, npages);
           inode->u.nfs_i.ncommit -= res;
           if ((inode->u.nfs_i.ncommit == 0) != list_empty(&inode->u.nfs_i.commit))
                   printk(KERN_ERR "NFS: desynchronized value of nfs_i.ncommit.\n");
           return res;
   }
   #endif
   
   
   /*
    * Try to update any existing write request, or create one if there is none.
    * In order to match, the request's credentials must match those of
    * the calling process.
    *
    * Note: Should always be called with the Page Lock held!
    */
   static struct nfs_page *
   nfs_update_request(struct file* file, struct inode *inode, struct page *page,
                      unsigned int offset, unsigned int bytes)
   {
           struct nfs_page         *req, *new = NULL;
           unsigned long           rqend, end;
   
           end = offset + bytes;
   
           for (;;) {
                   /* Loop over all inode entries and see if we find
                    * A request for the page we wish to update
                    */
                   spin_lock(&nfs_wreq_lock);
                   req = _nfs_find_request(inode, page);
                   if (req) {
                           if (!nfs_lock_request_dontget(req)) {
                                   int error;
                                   spin_unlock(&nfs_wreq_lock);
                                   error = nfs_wait_on_request(req);
                                   nfs_release_request(req);
                                   if (error < 0)
                                           return ERR_PTR(error);
                                   continue;
                           }
                           spin_unlock(&nfs_wreq_lock);
                           if (new)
                                   nfs_release_request(new);
                           break;
                   }
   
                   if (new) {
                           nfs_lock_request_dontget(new);
                           nfs_inode_add_request(inode, new);
                           spin_unlock(&nfs_wreq_lock);
                           nfs_mark_request_dirty(new);
                           return new;
                   }
                   spin_unlock(&nfs_wreq_lock);
   
                   new = nfs_create_request(nfs_file_cred(file), inode, page, offset, bytes);
                   if (IS_ERR(new))
                           return new;
                   if (file) {
                           new->wb_file = file;
                           get_file(file);
                   }
                   /* If the region is locked, adjust the timeout */
                   if (region_locked(inode, new))
                           new->wb_timeout = jiffies + NFS_WRITEBACK_LOCKDELAY;
                   else
                           new->wb_timeout = jiffies + NFS_WRITEBACK_DELAY;
           }
   
           /* We have a request for our page.
            * If the creds don't match, or the
            * page addresses don't match,
            * tell the caller to wait on the conflicting
            * request.
            */
           rqend = req->wb_offset + req->wb_bytes;
           if (req->wb_file != file
               || req->wb_page != page
               || !nfs_dirty_request(req)
               || offset > rqend || end < req->wb_offset) {
                   nfs_unlock_request(req);
                   return ERR_PTR(-EBUSY);
           }
   
           /* Okay, the request matches. Update the region */
           if (offset < req->wb_offset) {
                   req->wb_offset = offset;
                   req->wb_bytes = rqend - req->wb_offset;
           }
   
           if (end > rqend)
                   req->wb_bytes = end - req->wb_offset;
   
           return req;
   }
   
   /*
    * This is the strategy routine for NFS.
    * It is called by nfs_updatepage whenever the user wrote up to the end
    * of a page.
    *
    * We always try to submit a set of requests in parallel so that the
    * server's write code can gather writes. This is mainly for the benefit
    * of NFSv2.
    *
    * We never submit more requests than we think the remote can handle.
    * For UDP sockets, we make sure we don't exceed the congestion window;
    * for TCP, we limit the number of requests to 8.
    *
    * NFS_STRATEGY_PAGES gives the minimum number of requests for NFSv2 that
    * should be sent out in one go. This is for the benefit of NFSv2 servers
    * that perform write gathering.
    *
    * FIXME: Different servers may have different sweet spots.
    * Record the average congestion window in server struct?
    */
   #define NFS_STRATEGY_PAGES      8
   static void
   nfs_strategy(struct inode *inode)
   {
           unsigned int    dirty, wpages;
   
           dirty  = inode->u.nfs_i.ndirty;
           wpages = NFS_SERVER(inode)->wpages;
   #ifdef CONFIG_NFS_V3
           if (NFS_PROTO(inode)->version == 2) {
                   if (dirty >= NFS_STRATEGY_PAGES * wpages)
                           nfs_flush_file(inode, NULL, 0, 0, 0);
           } else if (dirty >= wpages)
                   nfs_flush_file(inode, NULL, 0, 0, 0);
   #else
           if (dirty >= NFS_STRATEGY_PAGES * wpages)
                   nfs_flush_file(inode, NULL, 0, 0, 0);
   #endif
   }
   
   int
   nfs_flush_incompatible(struct file *file, struct page *page)
   {
           struct rpc_cred *cred = nfs_file_cred(file);
           struct inode    *inode = page->mapping->host;
           struct nfs_page *req;
           int             status = 0;
           /*
            * Look for a request corresponding to this page. If there
            * is one, and it belongs to another file, we flush it out
            * before we try to copy anything into the page. Do this
            * due to the lack of an ACCESS-type call in NFSv2.
            * Also do the same if we find a request from an existing
            * dropped page.
            */
           req = nfs_find_request(inode,page);
           if (req) {
                   if (req->wb_file != file || req->wb_cred != cred || req->wb_page != page)
                           status = nfs_wb_page(inode, page);
                   nfs_release_request(req);
           }
           return (status < 0) ? status : 0;
   }
   
   /*
    * Update and possibly write a cached page of an NFS file.
    *
    * XXX: Keep an eye on generic_file_read to make sure it doesn't do bad
    * things with a page scheduled for an RPC call (e.g. invalidate it).
    */
   int
   nfs_updatepage(struct file *file, struct page *page, unsigned int offset, unsigned int count)
   {
           struct dentry   *dentry = file->f_dentry;
           struct inode    *inode = page->mapping->host;
           struct nfs_page *req;
           loff_t          end;
           int             status = 0;
   
           dprintk("NFS:      nfs_updatepage(%s/%s %d@%Ld)\n",
                   dentry->d_parent->d_name.name, dentry->d_name.name,
                   count, (long long)(page_offset(page) +offset));
   
           /*
            * If wsize is smaller than page size, update and write
            * page synchronously.
            */
           if (NFS_SERVER(inode)->wsize < PAGE_CACHE_SIZE || IS_SYNC(inode)) {
                   status = nfs_writepage_sync(file, inode, page, offset, count);
                   if (status > 0) {
                           if (offset == 0 && status == PAGE_CACHE_SIZE)
                                   SetPageUptodate(page);
                           return 0;
                   }
                   return status;
           }
   
           /*
            * Try to find an NFS request corresponding to this page
            * and update it.
            * If the existing request cannot be updated, we must flush
            * it out now.
            */
           do {
                   req = nfs_update_request(file, inode, page, offset, count);
                   status = (IS_ERR(req)) ? PTR_ERR(req) : 0;
                   if (status != -EBUSY)
                           break;
                   /* Request could not be updated. Flush it out and try again */
                   status = nfs_wb_page(inode, page);
           } while (status >= 0);
           if (status < 0)
                   goto done;
   
           status = 0;
           end = ((loff_t)page->index<<PAGE_CACHE_SHIFT) + (loff_t)(offset + count);
           if (inode->i_size < end)
                   inode->i_size = end;
   
           /* If we wrote past the end of the page.
            * Call the strategy routine so it can send out a bunch
            * of requests.
            */
           if (req->wb_offset == 0 && req->wb_bytes == PAGE_CACHE_SIZE) {
                   SetPageUptodate(page);
                   nfs_unlock_request(req);
                   nfs_strategy(inode);
           } else
                   nfs_unlock_request(req);
   done:
           dprintk("NFS:      nfs_updatepage returns %d (isize %Ld)\n",
                                                   status, (long long)inode->i_size);
           if (status < 0)
                   ClearPageUptodate(page);
           return status;
   }
   
   /*
    * Set up the argument/result storage required for the RPC call.
    */
   static void
   nfs_write_rpcsetup(struct list_head *head, struct nfs_write_data *data)
   {
           struct nfs_page         *req;
           struct page             **pages;
           unsigned int            count;
   
           /* Set up the RPC argument and reply structs
            * NB: take care not to mess about with data->commit et al. */
   
           pages = data->args.pages;
           count = 0;
           while (!list_empty(head)) {
                   struct nfs_page *req = nfs_list_entry(head->next);
                   nfs_list_remove_request(req);
                   nfs_list_add_request(req, &data->pages);
                   *pages++ = req->wb_page;
                   count += req->wb_bytes;
           }
           req = nfs_list_entry(data->pages.next);
           data->inode = req->wb_inode;
           data->cred = req->wb_cred;
           data->args.fh     = NFS_FH(req->wb_inode);
           data->args.offset = page_offset(req->wb_page) + req->wb_offset;
           data->args.pgbase = req->wb_offset;
           data->args.count  = count;
           data->res.fattr   = &data->fattr;
           data->res.count   = count;
           data->res.verf    = &data->verf;
   }
   
   
   /*
    * Create an RPC task for the given write request and kick it.
    * The page must have been locked by the caller.
    *
    * It may happen that the page we're passed is not marked dirty.
    * This is the case if nfs_updatepage detects a conflicting request
    * that has been written but not committed.
    */
   static int
   nfs_flush_one(struct list_head *head, struct inode *inode, int how)
   {
           struct rpc_clnt         *clnt = NFS_CLIENT(inode);
           struct nfs_write_data   *data;
           struct rpc_task         *task;
           struct rpc_message      msg;
           int                     flags,
                                   nfsvers = NFS_PROTO(inode)->version,
                                   async = !(how & FLUSH_SYNC),
                                   stable = (how & FLUSH_STABLE);
           sigset_t                oldset;
   
   
           data = nfs_writedata_alloc();
           if (!data)
                   goto out_bad;
           task = &data->task;
   
           /* Set the initial flags for the task.  */
           flags = (async) ? RPC_TASK_ASYNC : 0;
   
           /* Set up the argument struct */
           nfs_write_rpcsetup(head, data);
           if (nfsvers < 3)
                   data->args.stable = NFS_FILE_SYNC;
           else if (stable) {
                   if (!inode->u.nfs_i.ncommit)
                           data->args.stable = NFS_FILE_SYNC;
                   else
                           data->args.stable = NFS_DATA_SYNC;
           } else
                   data->args.stable = NFS_UNSTABLE;
   
           /* Finalize the task. */
           rpc_init_task(task, clnt, nfs_writeback_done, flags);
           task->tk_calldata = data;
           /* Release requests */
           task->tk_release = nfs_writedata_release;
   
   #ifdef CONFIG_NFS_V3
           msg.rpc_proc = (nfsvers == 3) ? NFS3PROC_WRITE : NFSPROC_WRITE;
   #else
           msg.rpc_proc = NFSPROC_WRITE;
   #endif
           msg.rpc_argp = &data->args;
           msg.rpc_resp = &data->res;
           msg.rpc_cred = data->cred;
   
           dprintk("NFS: %4d initiated write call (req %x/%Ld count %u)\n",
                   task->tk_pid, 
                   inode->i_dev,
                   (long long)NFS_FILEID(inode),
                   data->args.count);
   
           rpc_clnt_sigmask(clnt, &oldset);
           rpc_call_setup(task, &msg, 0);
           lock_kernel();
           rpc_execute(task);
           unlock_kernel();
           rpc_clnt_sigunmask(clnt, &oldset);
           return 0;
    out_bad:
           while (!list_empty(head)) {
                   struct nfs_page *req = nfs_list_entry(head->next);
                   nfs_list_remove_request(req);
                   nfs_mark_request_dirty(req);
                   nfs_unlock_request(req);
           }
           return -ENOMEM;
   }
   
   int
   nfs_flush_list(struct list_head *head, int wpages, int how)
   {
           LIST_HEAD(one_request);
           struct nfs_page         *req;
           int                     error = 0;
           unsigned int            pages = 0;
   
           while (!list_empty(head)) {
                   pages += nfs_coalesce_requests(head, &one_request, wpages);
                   req = nfs_list_entry(one_request.next);
                   error = nfs_flush_one(&one_request, req->wb_inode, how);
                   if (error < 0)
                           break;
           }
           if (error >= 0)
                   return pages;
   
           while (!list_empty(head)) {
                   req = nfs_list_entry(head->next);
                   nfs_list_remove_request(req);
                   nfs_mark_request_dirty(req);
                   nfs_unlock_request(req);
           }
           return error;
   }
   
   
   /*
    * This function is called when the WRITE call is complete.
    */
   static void
   nfs_writeback_done(struct rpc_task *task)
   {
           struct nfs_write_data   *data = (struct nfs_write_data *) task->tk_calldata;
           struct nfs_writeargs    *argp = &data->args;
           struct nfs_writeres     *resp = &data->res;
          struct inode            *inode = data->inode;
          struct nfs_page         *req;
          struct page             *page;
  
          dprintk("NFS: %4d nfs_writeback_done (status %d)\n",
                  task->tk_pid, task->tk_status);
  
          if (nfs_async_handle_jukebox(task))
                  return;
  
          /* We can't handle that yet but we check for it nevertheless */
          if (resp->count < argp->count && task->tk_status >= 0) {
                  static unsigned long    complain;
                  if (time_before(complain, jiffies)) {
                          printk(KERN_WARNING
                                 "NFS: Server wrote less than requested.\n");
                          complain = jiffies + 300 * HZ;
                  }
                  /* Can't do anything about it right now except throw
                   * an error. */
                  task->tk_status = -EIO;
          }
  #ifdef CONFIG_NFS_V3
          if (resp->verf->committed < argp->stable && task->tk_status >= 0) {
                  /* We tried a write call, but the server did not
                   * commit data to stable storage even though we
                   * requested it.
                   * Note: There is a known bug in Tru64 < 5.0 in which
                   *       the server reports NFS_DATA_SYNC, but performs
                   *       NFS_FILE_SYNC. We therefore implement this checking
                   *       as a dprintk() in order to avoid filling syslog.
                   */
                  static unsigned long    complain;
  
                  if (time_before(complain, jiffies)) {
                          dprintk("NFS: faulty NFSv3 server %s:"
                                  " (committed = %d) != (stable = %d)\n",
                                  NFS_SERVER(inode)->hostname,
                                  resp->verf->committed, argp->stable);
                          complain = jiffies + 300 * HZ;
                  }
          }
  #endif
  
          /*
           * Update attributes as result of writeback.
           * FIXME: There is an inherent race with invalidate_inode_pages and
           *        writebacks since the page->count is kept > 1 for as long
           *        as the page has a write request pending.
           */
          nfs_write_attributes(inode, resp->fattr);
          while (!list_empty(&data->pages)) {
                  req = nfs_list_entry(data->pages.next);
                  nfs_list_remove_request(req);
                  page = req->wb_page;
  
                  dprintk("NFS: write (%x/%Ld %d@%Ld)",
                          req->wb_inode->i_dev,
                          (long long)NFS_FILEID(req->wb_inode),
                          req->wb_bytes,
                          (long long)(page_offset(page) + req->wb_offset));
  
                  if (task->tk_status < 0) {
                          ClearPageUptodate(page);
                          SetPageError(page);
                          if (req->wb_file)
                                  req->wb_file->f_error = task->tk_status;
                          nfs_inode_remove_request(req);
                          dprintk(", error = %d\n", task->tk_status);
                          goto next;
                  }
  
  #ifdef CONFIG_NFS_V3
                  if (argp->stable != NFS_UNSTABLE || resp->verf->committed == NFS_FILE_SYNC) {
                          nfs_inode_remove_request(req);
                          dprintk(" OK\n");
                          goto next;
                  }
                  memcpy(&req->wb_verf, resp->verf, sizeof(req->wb_verf));
                  req->wb_timeout = jiffies + NFS_COMMIT_DELAY;
                  nfs_mark_request_commit(req);
                  dprintk(" marked for commit\n");
  #else
                  nfs_inode_remove_request(req);
  #endif
          next:
                  nfs_unlock_request(req);
          }
  }
  
  
  #ifdef CONFIG_NFS_V3
  /*
   * Set up the argument/result storage required for the RPC call.
   */
  static void
  nfs_commit_rpcsetup(struct list_head *head, struct nfs_write_data *data)
  {
          struct nfs_page         *first, *last;
          struct inode            *inode;
          loff_t                  start, end, len;
  
          /* Set up the RPC argument and reply structs
           * NB: take care not to mess about with data->commit et al. */
  
          list_splice(head, &data->pages);
          INIT_LIST_HEAD(head);
          first = nfs_list_entry(data->pages.next);
          last = nfs_list_entry(data->pages.prev);
          inode = first->wb_inode;
  
          /*
           * Determine the offset range of requests in the COMMIT call.
           * We rely on the fact that data->pages is an ordered list...
           */
          start = page_offset(first->wb_page) + first->wb_offset;
          end = page_offset(last->wb_page) + (last->wb_offset + last->wb_bytes);
          len = end - start;
          /* If 'len' is not a 32-bit quantity, pass '' in the COMMIT call */
          if (end >= inode->i_size || len < 0 || len > (~((u32)0) >> 1))
                  len = 0;
  
          data->inode       = inode;
          data->cred        = first->wb_cred;
          data->args.fh     = NFS_FH(inode);
          data->args.offset = start;
          data->res.count   = data->args.count = (u32)len;
          data->res.fattr   = &data->fattr;
          data->res.verf    = &data->verf;
  }
  
  /*
   * Commit dirty pages
   */
  int
  nfs_commit_list(struct list_head *head, int how)
  {
          struct rpc_message      msg;
          struct rpc_clnt         *clnt;
          struct nfs_write_data   *data;
          struct rpc_task         *task;
          struct nfs_page         *req;
          int                     flags,
                                  async = !(how & FLUSH_SYNC);
          sigset_t                oldset;
  
          data = nfs_writedata_alloc();
  
          if (!data)
                  goto out_bad;
          task = &data->task;
  
          flags = (async) ? RPC_TASK_ASYNC : 0;
  
          /* Set up the argument struct */
          nfs_commit_rpcsetup(head, data);
          req = nfs_list_entry(data->pages.next);
          clnt = NFS_CLIENT(req->wb_inode);
  
          rpc_init_task(task, clnt, nfs_commit_done, flags);
          task->tk_calldata = data;
          /* Release requests */
          task->tk_release = nfs_writedata_release;
  
          msg.rpc_proc = NFS3PROC_COMMIT;
          msg.rpc_argp = &data->args;
          msg.rpc_resp = &data->res;
          msg.rpc_cred = data->cred;
  
          dprintk("NFS: %4d initiated commit call\n", task->tk_pid);
          rpc_clnt_sigmask(clnt, &oldset);
          rpc_call_setup(task, &msg, 0);
          lock_kernel();
          rpc_execute(task);
          unlock_kernel();
          rpc_clnt_sigunmask(clnt, &oldset);
          return 0;
   out_bad:
          while (!list_empty(head)) {
                  req = nfs_list_entry(head->next);
                  nfs_list_remove_request(req);
                  nfs_mark_request_commit(req);
                  nfs_unlock_request(req);
          }
          return -ENOMEM;
  }
  
  /*
   * COMMIT call returned
   */
  static void
  nfs_commit_done(struct rpc_task *task)
  {
          struct nfs_write_data   *data = (struct nfs_write_data *)task->tk_calldata;
          struct nfs_writeres     *resp = &data->res;
          struct nfs_page         *req;
          struct inode            *inode = data->inode;
  
          dprintk("NFS: %4d nfs_commit_done (status %d)\n",
                                  task->tk_pid, task->tk_status);
  
          if (nfs_async_handle_jukebox(task))
                  return;
  
          nfs_write_attributes(inode, resp->fattr);
          while (!list_empty(&data->pages)) {
                  req = nfs_list_entry(data->pages.next);
                  nfs_list_remove_request(req);
  
                  dprintk("NFS: commit (%x/%Ld %d@%Ld)",
                          req->wb_inode->i_dev,
                          (long long)NFS_FILEID(req->wb_inode),
                          req->wb_bytes,
                          (long long)(page_offset(req->wb_page) + req->wb_offset));
                  if (task->tk_status < 0) {
                          if (req->wb_file)
                                  req->wb_file->f_error = task->tk_status;
                          nfs_inode_remove_request(req);
                          dprintk(", error = %d\n", task->tk_status);
                          goto next;
                  }
  
                  /* Okay, COMMIT succeeded, apparently. Check the verifier
                   * returned by the server against all stored verfs. */
                  if (!memcmp(req->wb_verf.verifier, data->verf.verifier, sizeof(data->verf.verifier))) {
                          /* We have a match */
                          nfs_inode_remove_request(req);
                          dprintk(" OK\n");
                          goto next;
                  }
                  /* We have a mismatch. Write the page again */
                  dprintk(" mismatch\n");
                  nfs_mark_request_dirty(req);
          next:
                  nfs_unlock_request(req);
          }
  }
  #endif
  
  int nfs_flush_file(struct inode *inode, struct file *file, unsigned long idx_start,
                     unsigned int npages, int how)
  {
          LIST_HEAD(head);
          int                     res,
                                  error = 0;
  
          spin_lock(&nfs_wreq_lock);
          res = nfs_scan_dirty(inode, &head, file, idx_start, npages);
          spin_unlock(&nfs_wreq_lock);
          if (res)
                  error = nfs_flush_list(&head, NFS_SERVER(inode)->wpages, how);
          if (error < 0)
                  return error;
          return res;
  }
  
  #ifdef CONFIG_NFS_V3
  int nfs_commit_file(struct inode *inode, struct file *file, unsigned long idx_start,
                      unsigned int npages, int how)
  {
          LIST_HEAD(head);
          int                     res,
                                  error = 0;
  
          spin_lock(&nfs_wreq_lock);
          res = nfs_scan_commit(inode, &head, file, idx_start, npages);
          spin_unlock(&nfs_wreq_lock);
          if (res)
                  error = nfs_commit_list(&head, how);
          if (error < 0)
                  return error;
          return res;
  }
  #endif
  
  int nfs_sync_file(struct inode *inode, struct file *file, unsigned long idx_start,
                    unsigned int npages, int how)
  {
          int     error,
                  wait;
  
          wait = how & FLUSH_WAIT;
          how &= ~FLUSH_WAIT;
  
          if (!inode && file)
                  inode = file->f_dentry->d_inode;
  
          do {
                  error = 0;
                  if (wait)
                          error = nfs_wait_on_requests(inode, file, idx_start, npages);
                  if (error == 0)
                          error = nfs_flush_file(inode, file, idx_start, npages, how);
  #ifdef CONFIG_NFS_V3
                  if (error == 0)
                          error = nfs_commit_file(inode, file, idx_start, npages, how);
  #endif
          } while (error > 0);
          return error;
  }
  
  int nfs_init_writepagecache(void)
  {
          nfs_wdata_cachep = kmem_cache_create("nfs_write_data",
                                               sizeof(struct nfs_write_data),
                                               0, SLAB_HWCACHE_ALIGN,
                                               NULL, NULL);
          if (nfs_wdata_cachep == NULL)
                  return -ENOMEM;
  
          return 0;
  }
  
  void nfs_destroy_writepagecache(void)
  {
          if (kmem_cache_destroy(nfs_wdata_cachep))
                  printk(KERN_INFO "nfs_write_data: not all structures were freed\n");
  }
  

Cache object: 9f2855e80a1c213fc96c7f8e2d0eea70