FreeBSD/Linux Kernel Cross Reference
sys/fs/file.c

     /*
      *  linux/fs/file.c
      *
      *  Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
      *
      *  Manage the dynamic fd arrays in the process files_struct.
      */
     
     #include <linux/syscalls.h>
    #include <linux/export.h>
    #include <linux/fs.h>
    #include <linux/mm.h>
    #include <linux/mmzone.h>
    #include <linux/time.h>
    #include <linux/sched.h>
    #include <linux/slab.h>
    #include <linux/vmalloc.h>
    #include <linux/file.h>
    #include <linux/fdtable.h>
    #include <linux/bitops.h>
    #include <linux/interrupt.h>
    #include <linux/spinlock.h>
    #include <linux/rcupdate.h>
    #include <linux/workqueue.h>
    
    struct fdtable_defer {
            spinlock_t lock;
            struct work_struct wq;
            struct fdtable *next;
    };
    
    int sysctl_nr_open __read_mostly = 1024*1024;
    int sysctl_nr_open_min = BITS_PER_LONG;
    int sysctl_nr_open_max = 1024 * 1024; /* raised later */
    
    /*
     * We use this list to defer free fdtables that have vmalloced
     * sets/arrays. By keeping a per-cpu list, we avoid having to embed
     * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
     * this per-task structure.
     */
    static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
    
    static void *alloc_fdmem(size_t size)
    {
            /*
             * Very large allocations can stress page reclaim, so fall back to
             * vmalloc() if the allocation size will be considered "large" by the VM.
             */
            if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
                    void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN);
                    if (data != NULL)
                            return data;
            }
            return vmalloc(size);
    }
    
    static void free_fdmem(void *ptr)
    {
            is_vmalloc_addr(ptr) ? vfree(ptr) : kfree(ptr);
    }
    
    static void __free_fdtable(struct fdtable *fdt)
    {
            free_fdmem(fdt->fd);
            free_fdmem(fdt->open_fds);
            kfree(fdt);
    }
    
    static void free_fdtable_work(struct work_struct *work)
    {
            struct fdtable_defer *f =
                    container_of(work, struct fdtable_defer, wq);
            struct fdtable *fdt;
    
            spin_lock_bh(&f->lock);
            fdt = f->next;
            f->next = NULL;
            spin_unlock_bh(&f->lock);
            while(fdt) {
                    struct fdtable *next = fdt->next;
    
                    __free_fdtable(fdt);
                    fdt = next;
            }
    }
    
    static void free_fdtable_rcu(struct rcu_head *rcu)
    {
            struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
            struct fdtable_defer *fddef;
    
            BUG_ON(!fdt);
            BUG_ON(fdt->max_fds <= NR_OPEN_DEFAULT);
    
            if (!is_vmalloc_addr(fdt->fd) && !is_vmalloc_addr(fdt->open_fds)) {
                    kfree(fdt->fd);
                    kfree(fdt->open_fds);
                    kfree(fdt);
           } else {
                   fddef = &get_cpu_var(fdtable_defer_list);
                   spin_lock(&fddef->lock);
                   fdt->next = fddef->next;
                   fddef->next = fdt;
                   /* vmallocs are handled from the workqueue context */
                   schedule_work(&fddef->wq);
                   spin_unlock(&fddef->lock);
                   put_cpu_var(fdtable_defer_list);
           }
   }
   
   /*
    * Expand the fdset in the files_struct.  Called with the files spinlock
    * held for write.
    */
   static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
   {
           unsigned int cpy, set;
   
           BUG_ON(nfdt->max_fds < ofdt->max_fds);
   
           cpy = ofdt->max_fds * sizeof(struct file *);
           set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
           memcpy(nfdt->fd, ofdt->fd, cpy);
           memset((char *)(nfdt->fd) + cpy, 0, set);
   
           cpy = ofdt->max_fds / BITS_PER_BYTE;
           set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
           memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
           memset((char *)(nfdt->open_fds) + cpy, 0, set);
           memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
           memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
   }
   
   static struct fdtable * alloc_fdtable(unsigned int nr)
   {
           struct fdtable *fdt;
           void *data;
   
           /*
            * Figure out how many fds we actually want to support in this fdtable.
            * Allocation steps are keyed to the size of the fdarray, since it
            * grows far faster than any of the other dynamic data. We try to fit
            * the fdarray into comfortable page-tuned chunks: starting at 1024B
            * and growing in powers of two from there on.
            */
           nr /= (1024 / sizeof(struct file *));
           nr = roundup_pow_of_two(nr + 1);
           nr *= (1024 / sizeof(struct file *));
           /*
            * Note that this can drive nr *below* what we had passed if sysctl_nr_open
            * had been set lower between the check in expand_files() and here.  Deal
            * with that in caller, it's cheaper that way.
            *
            * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
            * bitmaps handling below becomes unpleasant, to put it mildly...
            */
           if (unlikely(nr > sysctl_nr_open))
                   nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;
   
           fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
           if (!fdt)
                   goto out;
           fdt->max_fds = nr;
           data = alloc_fdmem(nr * sizeof(struct file *));
           if (!data)
                   goto out_fdt;
           fdt->fd = data;
   
           data = alloc_fdmem(max_t(size_t,
                                    2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
           if (!data)
                   goto out_arr;
           fdt->open_fds = data;
           data += nr / BITS_PER_BYTE;
           fdt->close_on_exec = data;
           fdt->next = NULL;
   
           return fdt;
   
   out_arr:
           free_fdmem(fdt->fd);
   out_fdt:
           kfree(fdt);
   out:
           return NULL;
   }
   
   /*
    * Expand the file descriptor table.
    * This function will allocate a new fdtable and both fd array and fdset, of
    * the given size.
    * Return <0 error code on error; 1 on successful completion.
    * The files->file_lock should be held on entry, and will be held on exit.
    */
   static int expand_fdtable(struct files_struct *files, int nr)
           __releases(files->file_lock)
           __acquires(files->file_lock)
   {
           struct fdtable *new_fdt, *cur_fdt;
   
           spin_unlock(&files->file_lock);
           new_fdt = alloc_fdtable(nr);
           spin_lock(&files->file_lock);
           if (!new_fdt)
                   return -ENOMEM;
           /*
            * extremely unlikely race - sysctl_nr_open decreased between the check in
            * caller and alloc_fdtable().  Cheaper to catch it here...
            */
           if (unlikely(new_fdt->max_fds <= nr)) {
                   __free_fdtable(new_fdt);
                   return -EMFILE;
           }
           /*
            * Check again since another task may have expanded the fd table while
            * we dropped the lock
            */
           cur_fdt = files_fdtable(files);
           if (nr >= cur_fdt->max_fds) {
                   /* Continue as planned */
                   copy_fdtable(new_fdt, cur_fdt);
                   rcu_assign_pointer(files->fdt, new_fdt);
                   if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
                           call_rcu(&cur_fdt->rcu, free_fdtable_rcu);
           } else {
                   /* Somebody else expanded, so undo our attempt */
                   __free_fdtable(new_fdt);
           }
           return 1;
   }
   
   /*
    * Expand files.
    * This function will expand the file structures, if the requested size exceeds
    * the current capacity and there is room for expansion.
    * Return <0 error code on error; 0 when nothing done; 1 when files were
    * expanded and execution may have blocked.
    * The files->file_lock should be held on entry, and will be held on exit.
    */
   static int expand_files(struct files_struct *files, int nr)
   {
           struct fdtable *fdt;
   
           fdt = files_fdtable(files);
   
           /* Do we need to expand? */
           if (nr < fdt->max_fds)
                   return 0;
   
           /* Can we expand? */
           if (nr >= sysctl_nr_open)
                   return -EMFILE;
   
           /* All good, so we try */
           return expand_fdtable(files, nr);
   }
   
   static inline void __set_close_on_exec(int fd, struct fdtable *fdt)
   {
           __set_bit(fd, fdt->close_on_exec);
   }
   
   static inline void __clear_close_on_exec(int fd, struct fdtable *fdt)
   {
           __clear_bit(fd, fdt->close_on_exec);
   }
   
   static inline void __set_open_fd(int fd, struct fdtable *fdt)
   {
           __set_bit(fd, fdt->open_fds);
   }
   
   static inline void __clear_open_fd(int fd, struct fdtable *fdt)
   {
           __clear_bit(fd, fdt->open_fds);
   }
   
   static int count_open_files(struct fdtable *fdt)
   {
           int size = fdt->max_fds;
           int i;
   
           /* Find the last open fd */
           for (i = size / BITS_PER_LONG; i > 0; ) {
                   if (fdt->open_fds[--i])
                           break;
           }
           i = (i + 1) * BITS_PER_LONG;
           return i;
   }
   
   /*
    * Allocate a new files structure and copy contents from the
    * passed in files structure.
    * errorp will be valid only when the returned files_struct is NULL.
    */
   struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
   {
           struct files_struct *newf;
           struct file **old_fds, **new_fds;
           int open_files, size, i;
           struct fdtable *old_fdt, *new_fdt;
   
           *errorp = -ENOMEM;
           newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
           if (!newf)
                   goto out;
   
           atomic_set(&newf->count, 1);
   
           spin_lock_init(&newf->file_lock);
           newf->next_fd = 0;
           new_fdt = &newf->fdtab;
           new_fdt->max_fds = NR_OPEN_DEFAULT;
           new_fdt->close_on_exec = newf->close_on_exec_init;
           new_fdt->open_fds = newf->open_fds_init;
           new_fdt->fd = &newf->fd_array[0];
           new_fdt->next = NULL;
   
           spin_lock(&oldf->file_lock);
           old_fdt = files_fdtable(oldf);
           open_files = count_open_files(old_fdt);
   
           /*
            * Check whether we need to allocate a larger fd array and fd set.
            */
           while (unlikely(open_files > new_fdt->max_fds)) {
                   spin_unlock(&oldf->file_lock);
   
                   if (new_fdt != &newf->fdtab)
                           __free_fdtable(new_fdt);
   
                   new_fdt = alloc_fdtable(open_files - 1);
                   if (!new_fdt) {
                           *errorp = -ENOMEM;
                           goto out_release;
                   }
   
                   /* beyond sysctl_nr_open; nothing to do */
                   if (unlikely(new_fdt->max_fds < open_files)) {
                           __free_fdtable(new_fdt);
                           *errorp = -EMFILE;
                           goto out_release;
                   }
   
                   /*
                    * Reacquire the oldf lock and a pointer to its fd table
                    * who knows it may have a new bigger fd table. We need
                    * the latest pointer.
                    */
                   spin_lock(&oldf->file_lock);
                   old_fdt = files_fdtable(oldf);
                   open_files = count_open_files(old_fdt);
           }
   
           old_fds = old_fdt->fd;
           new_fds = new_fdt->fd;
   
           memcpy(new_fdt->open_fds, old_fdt->open_fds, open_files / 8);
           memcpy(new_fdt->close_on_exec, old_fdt->close_on_exec, open_files / 8);
   
           for (i = open_files; i != 0; i--) {
                   struct file *f = *old_fds++;
                   if (f) {
                           get_file(f);
                   } else {
                           /*
                            * The fd may be claimed in the fd bitmap but not yet
                            * instantiated in the files array if a sibling thread
                            * is partway through open().  So make sure that this
                            * fd is available to the new process.
                            */
                           __clear_open_fd(open_files - i, new_fdt);
                   }
                   rcu_assign_pointer(*new_fds++, f);
           }
           spin_unlock(&oldf->file_lock);
   
           /* compute the remainder to be cleared */
           size = (new_fdt->max_fds - open_files) * sizeof(struct file *);
   
           /* This is long word aligned thus could use a optimized version */
           memset(new_fds, 0, size);
   
           if (new_fdt->max_fds > open_files) {
                   int left = (new_fdt->max_fds - open_files) / 8;
                   int start = open_files / BITS_PER_LONG;
   
                   memset(&new_fdt->open_fds[start], 0, left);
                   memset(&new_fdt->close_on_exec[start], 0, left);
           }
   
           rcu_assign_pointer(newf->fdt, new_fdt);
   
           return newf;
   
   out_release:
           kmem_cache_free(files_cachep, newf);
   out:
           return NULL;
   }
   
   static void close_files(struct files_struct * files)
   {
           int i, j;
           struct fdtable *fdt;
   
           j = 0;
   
           /*
            * It is safe to dereference the fd table without RCU or
            * ->file_lock because this is the last reference to the
            * files structure.  But use RCU to shut RCU-lockdep up.
            */
           rcu_read_lock();
           fdt = files_fdtable(files);
           rcu_read_unlock();
           for (;;) {
                   unsigned long set;
                   i = j * BITS_PER_LONG;
                   if (i >= fdt->max_fds)
                           break;
                   set = fdt->open_fds[j++];
                   while (set) {
                           if (set & 1) {
                                   struct file * file = xchg(&fdt->fd[i], NULL);
                                   if (file) {
                                           filp_close(file, files);
                                           cond_resched();
                                   }
                           }
                           i++;
                           set >>= 1;
                   }
           }
   }
   
   struct files_struct *get_files_struct(struct task_struct *task)
   {
           struct files_struct *files;
   
           task_lock(task);
           files = task->files;
           if (files)
                   atomic_inc(&files->count);
           task_unlock(task);
   
           return files;
   }
   
   void put_files_struct(struct files_struct *files)
   {
           struct fdtable *fdt;
   
           if (atomic_dec_and_test(&files->count)) {
                   close_files(files);
                   /* not really needed, since nobody can see us */
                   rcu_read_lock();
                   fdt = files_fdtable(files);
                   rcu_read_unlock();
                   /* free the arrays if they are not embedded */
                   if (fdt != &files->fdtab)
                           __free_fdtable(fdt);
                   kmem_cache_free(files_cachep, files);
           }
   }
   
   void reset_files_struct(struct files_struct *files)
   {
           struct task_struct *tsk = current;
           struct files_struct *old;
   
           old = tsk->files;
           task_lock(tsk);
           tsk->files = files;
           task_unlock(tsk);
           put_files_struct(old);
   }
   
   void exit_files(struct task_struct *tsk)
   {
           struct files_struct * files = tsk->files;
   
           if (files) {
                   task_lock(tsk);
                   tsk->files = NULL;
                   task_unlock(tsk);
                   put_files_struct(files);
           }
   }
   
   static void fdtable_defer_list_init(int cpu)
   {
           struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
           spin_lock_init(&fddef->lock);
           INIT_WORK(&fddef->wq, free_fdtable_work);
           fddef->next = NULL;
   }
   
   void __init files_defer_init(void)
   {
           int i;
           for_each_possible_cpu(i)
                   fdtable_defer_list_init(i);
           sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) &
                                -BITS_PER_LONG;
   }
   
   struct files_struct init_files = {
           .count          = ATOMIC_INIT(1),
           .fdt            = &init_files.fdtab,
           .fdtab          = {
                   .max_fds        = NR_OPEN_DEFAULT,
                   .fd             = &init_files.fd_array[0],
                   .close_on_exec  = init_files.close_on_exec_init,
                   .open_fds       = init_files.open_fds_init,
           },
           .file_lock      = __SPIN_LOCK_UNLOCKED(init_task.file_lock),
   };
   
   /*
    * allocate a file descriptor, mark it busy.
    */
   int __alloc_fd(struct files_struct *files,
                  unsigned start, unsigned end, unsigned flags)
   {
           unsigned int fd;
           int error;
           struct fdtable *fdt;
   
           spin_lock(&files->file_lock);
   repeat:
           fdt = files_fdtable(files);
           fd = start;
           if (fd < files->next_fd)
                   fd = files->next_fd;
   
           if (fd < fdt->max_fds)
                   fd = find_next_zero_bit(fdt->open_fds, fdt->max_fds, fd);
   
           /*
            * N.B. For clone tasks sharing a files structure, this test
            * will limit the total number of files that can be opened.
            */
           error = -EMFILE;
           if (fd >= end)
                   goto out;
   
           error = expand_files(files, fd);
           if (error < 0)
                   goto out;
   
           /*
            * If we needed to expand the fs array we
            * might have blocked - try again.
            */
           if (error)
                   goto repeat;
   
           if (start <= files->next_fd)
                   files->next_fd = fd + 1;
   
           __set_open_fd(fd, fdt);
           if (flags & O_CLOEXEC)
                   __set_close_on_exec(fd, fdt);
           else
                   __clear_close_on_exec(fd, fdt);
           error = fd;
   #if 1
           /* Sanity check */
           if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
                   printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
                   rcu_assign_pointer(fdt->fd[fd], NULL);
           }
   #endif
   
   out:
           spin_unlock(&files->file_lock);
           return error;
   }
   
   static int alloc_fd(unsigned start, unsigned flags)
   {
           return __alloc_fd(current->files, start, rlimit(RLIMIT_NOFILE), flags);
   }
   
   int get_unused_fd_flags(unsigned flags)
   {
           return __alloc_fd(current->files, 0, rlimit(RLIMIT_NOFILE), flags);
   }
   EXPORT_SYMBOL(get_unused_fd_flags);
   
   static void __put_unused_fd(struct files_struct *files, unsigned int fd)
   {
           struct fdtable *fdt = files_fdtable(files);
           __clear_open_fd(fd, fdt);
           if (fd < files->next_fd)
                   files->next_fd = fd;
   }
   
   void put_unused_fd(unsigned int fd)
   {
           struct files_struct *files = current->files;
           spin_lock(&files->file_lock);
           __put_unused_fd(files, fd);
           spin_unlock(&files->file_lock);
   }
   
   EXPORT_SYMBOL(put_unused_fd);
   
   /*
    * Install a file pointer in the fd array.
    *
    * The VFS is full of places where we drop the files lock between
    * setting the open_fds bitmap and installing the file in the file
    * array.  At any such point, we are vulnerable to a dup2() race
    * installing a file in the array before us.  We need to detect this and
    * fput() the struct file we are about to overwrite in this case.
    *
    * It should never happen - if we allow dup2() do it, _really_ bad things
    * will follow.
    *
    * NOTE: __fd_install() variant is really, really low-level; don't
    * use it unless you are forced to by truly lousy API shoved down
    * your throat.  'files' *MUST* be either current->files or obtained
    * by get_files_struct(current) done by whoever had given it to you,
    * or really bad things will happen.  Normally you want to use
    * fd_install() instead.
    */
   
   void __fd_install(struct files_struct *files, unsigned int fd,
                   struct file *file)
   {
           struct fdtable *fdt;
           spin_lock(&files->file_lock);
           fdt = files_fdtable(files);
           BUG_ON(fdt->fd[fd] != NULL);
           rcu_assign_pointer(fdt->fd[fd], file);
           spin_unlock(&files->file_lock);
   }
   
   void fd_install(unsigned int fd, struct file *file)
   {
           __fd_install(current->files, fd, file);
   }
   
   EXPORT_SYMBOL(fd_install);
   
   /*
    * The same warnings as for __alloc_fd()/__fd_install() apply here...
    */
   int __close_fd(struct files_struct *files, unsigned fd)
   {
           struct file *file;
           struct fdtable *fdt;
   
           spin_lock(&files->file_lock);
           fdt = files_fdtable(files);
           if (fd >= fdt->max_fds)
                   goto out_unlock;
           file = fdt->fd[fd];
           if (!file)
                   goto out_unlock;
           rcu_assign_pointer(fdt->fd[fd], NULL);
           __clear_close_on_exec(fd, fdt);
           __put_unused_fd(files, fd);
           spin_unlock(&files->file_lock);
           return filp_close(file, files);
   
   out_unlock:
           spin_unlock(&files->file_lock);
           return -EBADF;
   }
   
   void do_close_on_exec(struct files_struct *files)
   {
           unsigned i;
           struct fdtable *fdt;
   
           /* exec unshares first */
           spin_lock(&files->file_lock);
           for (i = 0; ; i++) {
                   unsigned long set;
                   unsigned fd = i * BITS_PER_LONG;
                   fdt = files_fdtable(files);
                   if (fd >= fdt->max_fds)
                           break;
                   set = fdt->close_on_exec[i];
                   if (!set)
                           continue;
                   fdt->close_on_exec[i] = 0;
                   for ( ; set ; fd++, set >>= 1) {
                           struct file *file;
                           if (!(set & 1))
                                   continue;
                           file = fdt->fd[fd];
                           if (!file)
                                   continue;
                           rcu_assign_pointer(fdt->fd[fd], NULL);
                           __put_unused_fd(files, fd);
                           spin_unlock(&files->file_lock);
                           filp_close(file, files);
                           cond_resched();
                           spin_lock(&files->file_lock);
                   }
   
           }
           spin_unlock(&files->file_lock);
   }
   
   struct file *fget(unsigned int fd)
   {
           struct file *file;
           struct files_struct *files = current->files;
   
           rcu_read_lock();
           file = fcheck_files(files, fd);
           if (file) {
                   /* File object ref couldn't be taken */
                   if (file->f_mode & FMODE_PATH ||
                       !atomic_long_inc_not_zero(&file->f_count))
                           file = NULL;
           }
           rcu_read_unlock();
   
           return file;
   }
   
   EXPORT_SYMBOL(fget);
   
   struct file *fget_raw(unsigned int fd)
   {
           struct file *file;
           struct files_struct *files = current->files;
   
           rcu_read_lock();
           file = fcheck_files(files, fd);
           if (file) {
                   /* File object ref couldn't be taken */
                   if (!atomic_long_inc_not_zero(&file->f_count))
                           file = NULL;
           }
           rcu_read_unlock();
   
           return file;
   }
   
   EXPORT_SYMBOL(fget_raw);
   
   /*
    * Lightweight file lookup - no refcnt increment if fd table isn't shared.
    *
    * You can use this instead of fget if you satisfy all of the following
    * conditions:
    * 1) You must call fput_light before exiting the syscall and returning control
    *    to userspace (i.e. you cannot remember the returned struct file * after
    *    returning to userspace).
    * 2) You must not call filp_close on the returned struct file * in between
    *    calls to fget_light and fput_light.
    * 3) You must not clone the current task in between the calls to fget_light
    *    and fput_light.
    *
    * The fput_needed flag returned by fget_light should be passed to the
    * corresponding fput_light.
    */
   struct file *fget_light(unsigned int fd, int *fput_needed)
   {
           struct file *file;
           struct files_struct *files = current->files;
   
           *fput_needed = 0;
           if (atomic_read(&files->count) == 1) {
                   file = fcheck_files(files, fd);
                   if (file && (file->f_mode & FMODE_PATH))
                           file = NULL;
           } else {
                   rcu_read_lock();
                   file = fcheck_files(files, fd);
                   if (file) {
                           if (!(file->f_mode & FMODE_PATH) &&
                               atomic_long_inc_not_zero(&file->f_count))
                                   *fput_needed = 1;
                           else
                                   /* Didn't get the reference, someone's freed */
                                   file = NULL;
                   }
                   rcu_read_unlock();
           }
   
           return file;
   }
   EXPORT_SYMBOL(fget_light);
   
   struct file *fget_raw_light(unsigned int fd, int *fput_needed)
   {
           struct file *file;
           struct files_struct *files = current->files;
   
           *fput_needed = 0;
           if (atomic_read(&files->count) == 1) {
                   file = fcheck_files(files, fd);
           } else {
                   rcu_read_lock();
                   file = fcheck_files(files, fd);
                   if (file) {
                           if (atomic_long_inc_not_zero(&file->f_count))
                                   *fput_needed = 1;
                           else
                                   /* Didn't get the reference, someone's freed */
                                   file = NULL;
                   }
                   rcu_read_unlock();
           }
   
           return file;
   }
   
   void set_close_on_exec(unsigned int fd, int flag)
   {
           struct files_struct *files = current->files;
           struct fdtable *fdt;
           spin_lock(&files->file_lock);
           fdt = files_fdtable(files);
           if (flag)
                   __set_close_on_exec(fd, fdt);
           else
                   __clear_close_on_exec(fd, fdt);
           spin_unlock(&files->file_lock);
   }
   
   bool get_close_on_exec(unsigned int fd)
   {
           struct files_struct *files = current->files;
           struct fdtable *fdt;
           bool res;
           rcu_read_lock();
           fdt = files_fdtable(files);
           res = close_on_exec(fd, fdt);
           rcu_read_unlock();
           return res;
   }
   
   static int do_dup2(struct files_struct *files,
           struct file *file, unsigned fd, unsigned flags)
   {
           struct file *tofree;
           struct fdtable *fdt;
   
           /*
            * We need to detect attempts to do dup2() over allocated but still
            * not finished descriptor.  NB: OpenBSD avoids that at the price of
            * extra work in their equivalent of fget() - they insert struct
            * file immediately after grabbing descriptor, mark it larval if
            * more work (e.g. actual opening) is needed and make sure that
            * fget() treats larval files as absent.  Potentially interesting,
            * but while extra work in fget() is trivial, locking implications
            * and amount of surgery on open()-related paths in VFS are not.
            * FreeBSD fails with -EBADF in the same situation, NetBSD "solution"
            * deadlocks in rather amusing ways, AFAICS.  All of that is out of
            * scope of POSIX or SUS, since neither considers shared descriptor
            * tables and this condition does not arise without those.
            */
           fdt = files_fdtable(files);
           tofree = fdt->fd[fd];
           if (!tofree && fd_is_open(fd, fdt))
                   goto Ebusy;
           get_file(file);
           rcu_assign_pointer(fdt->fd[fd], file);
           __set_open_fd(fd, fdt);
           if (flags & O_CLOEXEC)
                   __set_close_on_exec(fd, fdt);
           else
                   __clear_close_on_exec(fd, fdt);
           spin_unlock(&files->file_lock);
   
           if (tofree)
                   filp_close(tofree, files);
   
           return fd;
   
   Ebusy:
           spin_unlock(&files->file_lock);
           return -EBUSY;
   }
   
   int replace_fd(unsigned fd, struct file *file, unsigned flags)
   {
           int err;
           struct files_struct *files = current->files;
   
           if (!file)
                   return __close_fd(files, fd);
   
           if (fd >= rlimit(RLIMIT_NOFILE))
                   return -EBADF;
   
           spin_lock(&files->file_lock);
           err = expand_files(files, fd);
           if (unlikely(err < 0))
                   goto out_unlock;
           return do_dup2(files, file, fd, flags);
   
   out_unlock:
           spin_unlock(&files->file_lock);
           return err;
   }
   
   SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
   {
           int err = -EBADF;
           struct file *file;
           struct files_struct *files = current->files;
   
           if ((flags & ~O_CLOEXEC) != 0)
                   return -EINVAL;
   
           if (unlikely(oldfd == newfd))
                   return -EINVAL;
   
           if (newfd >= rlimit(RLIMIT_NOFILE))
                   return -EBADF;
   
           spin_lock(&files->file_lock);
           err = expand_files(files, newfd);
           file = fcheck(oldfd);
           if (unlikely(!file))
                   goto Ebadf;
           if (unlikely(err < 0)) {
                   if (err == -EMFILE)
                           goto Ebadf;
                   goto out_unlock;
           }
           return do_dup2(files, file, newfd, flags);
   
   Ebadf:
           err = -EBADF;
   out_unlock:
           spin_unlock(&files->file_lock);
           return err;
   }
   
   SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)
   {
           if (unlikely(newfd == oldfd)) { /* corner case */
                   struct files_struct *files = current->files;
                   int retval = oldfd;
   
                   rcu_read_lock();
                   if (!fcheck_files(files, oldfd))
                           retval = -EBADF;
                   rcu_read_unlock();
                   return retval;
           }
           return sys_dup3(oldfd, newfd, 0);
   }
   
   SYSCALL_DEFINE1(dup, unsigned int, fildes)
   {
           int ret = -EBADF;
           struct file *file = fget_raw(fildes);
   
           if (file) {
                   ret = get_unused_fd();
                   if (ret >= 0)
                           fd_install(ret, file);
                   else
                           fput(file);
           }
           return ret;
   }
   
   int f_dupfd(unsigned int from, struct file *file, unsigned flags)
   {
           int err;
           if (from >= rlimit(RLIMIT_NOFILE))
                   return -EINVAL;
           err = alloc_fd(from, flags);
           if (err >= 0) {
                   get_file(file);
                   fd_install(err, file);
           }
           return err;
   }
   
   int iterate_fd(struct files_struct *files, unsigned n,
                   int (*f)(const void *, struct file *, unsigned),
                   const void *p)
   {
           struct fdtable *fdt;
           int res = 0;
           if (!files)
                   return 0;
           spin_lock(&files->file_lock);
           for (fdt = files_fdtable(files); n < fdt->max_fds; n++) {
                   struct file *file;
                   file = rcu_dereference_check_fdtable(files, fdt->fd[n]);
                   if (!file)
                           continue;
                  res = f(p, file, n);
                  if (res)
                          break;
          }
          spin_unlock(&files->file_lock);
          return res;
  }
  EXPORT_SYMBOL(iterate_fd);

Cache object: d54317bfb3f7bcdc4ccbfce92b0788a0