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![Al Viro](/assets/img/avatar_default.png)
New primitive: alloc_fd(start, flags). get_unused_fd() and get_unused_fd_flags() become wrappers on top of it. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
495 lines
12 KiB
C
495 lines
12 KiB
C
/*
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* linux/fs/file.c
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*
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* Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
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*
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* Manage the dynamic fd arrays in the process files_struct.
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*/
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#include <linux/module.h>
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#include <linux/fs.h>
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#include <linux/mm.h>
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#include <linux/time.h>
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#include <linux/slab.h>
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#include <linux/vmalloc.h>
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#include <linux/file.h>
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#include <linux/fdtable.h>
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#include <linux/bitops.h>
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#include <linux/interrupt.h>
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#include <linux/spinlock.h>
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#include <linux/rcupdate.h>
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#include <linux/workqueue.h>
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struct fdtable_defer {
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spinlock_t lock;
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struct work_struct wq;
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struct fdtable *next;
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};
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int sysctl_nr_open __read_mostly = 1024*1024;
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int sysctl_nr_open_min = BITS_PER_LONG;
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int sysctl_nr_open_max = 1024 * 1024; /* raised later */
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/*
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* We use this list to defer free fdtables that have vmalloced
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* sets/arrays. By keeping a per-cpu list, we avoid having to embed
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* the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
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* this per-task structure.
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*/
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static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
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static inline void * alloc_fdmem(unsigned int size)
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{
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if (size <= PAGE_SIZE)
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return kmalloc(size, GFP_KERNEL);
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else
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return vmalloc(size);
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}
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static inline void free_fdarr(struct fdtable *fdt)
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{
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if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *)))
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kfree(fdt->fd);
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else
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vfree(fdt->fd);
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}
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static inline void free_fdset(struct fdtable *fdt)
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{
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if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2))
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kfree(fdt->open_fds);
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else
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vfree(fdt->open_fds);
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}
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static void free_fdtable_work(struct work_struct *work)
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{
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struct fdtable_defer *f =
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container_of(work, struct fdtable_defer, wq);
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struct fdtable *fdt;
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spin_lock_bh(&f->lock);
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fdt = f->next;
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f->next = NULL;
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spin_unlock_bh(&f->lock);
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while(fdt) {
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struct fdtable *next = fdt->next;
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vfree(fdt->fd);
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free_fdset(fdt);
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kfree(fdt);
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fdt = next;
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}
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}
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void free_fdtable_rcu(struct rcu_head *rcu)
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{
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struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
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struct fdtable_defer *fddef;
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BUG_ON(!fdt);
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if (fdt->max_fds <= NR_OPEN_DEFAULT) {
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/*
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* This fdtable is embedded in the files structure and that
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* structure itself is getting destroyed.
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*/
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kmem_cache_free(files_cachep,
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container_of(fdt, struct files_struct, fdtab));
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return;
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}
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if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) {
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kfree(fdt->fd);
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kfree(fdt->open_fds);
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kfree(fdt);
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} else {
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fddef = &get_cpu_var(fdtable_defer_list);
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spin_lock(&fddef->lock);
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fdt->next = fddef->next;
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fddef->next = fdt;
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/* vmallocs are handled from the workqueue context */
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schedule_work(&fddef->wq);
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spin_unlock(&fddef->lock);
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put_cpu_var(fdtable_defer_list);
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}
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}
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/*
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* Expand the fdset in the files_struct. Called with the files spinlock
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* held for write.
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*/
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static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
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{
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unsigned int cpy, set;
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BUG_ON(nfdt->max_fds < ofdt->max_fds);
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cpy = ofdt->max_fds * sizeof(struct file *);
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set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
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memcpy(nfdt->fd, ofdt->fd, cpy);
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memset((char *)(nfdt->fd) + cpy, 0, set);
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cpy = ofdt->max_fds / BITS_PER_BYTE;
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set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
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memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
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memset((char *)(nfdt->open_fds) + cpy, 0, set);
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memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
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memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
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}
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static struct fdtable * alloc_fdtable(unsigned int nr)
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{
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struct fdtable *fdt;
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char *data;
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/*
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* Figure out how many fds we actually want to support in this fdtable.
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* Allocation steps are keyed to the size of the fdarray, since it
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* grows far faster than any of the other dynamic data. We try to fit
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* the fdarray into comfortable page-tuned chunks: starting at 1024B
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* and growing in powers of two from there on.
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*/
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nr /= (1024 / sizeof(struct file *));
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nr = roundup_pow_of_two(nr + 1);
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nr *= (1024 / sizeof(struct file *));
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/*
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* Note that this can drive nr *below* what we had passed if sysctl_nr_open
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* had been set lower between the check in expand_files() and here. Deal
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* with that in caller, it's cheaper that way.
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*
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* We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
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* bitmaps handling below becomes unpleasant, to put it mildly...
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*/
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if (unlikely(nr > sysctl_nr_open))
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nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;
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fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
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if (!fdt)
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goto out;
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fdt->max_fds = nr;
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data = alloc_fdmem(nr * sizeof(struct file *));
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if (!data)
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goto out_fdt;
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fdt->fd = (struct file **)data;
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data = alloc_fdmem(max_t(unsigned int,
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2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
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if (!data)
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goto out_arr;
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fdt->open_fds = (fd_set *)data;
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data += nr / BITS_PER_BYTE;
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fdt->close_on_exec = (fd_set *)data;
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INIT_RCU_HEAD(&fdt->rcu);
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fdt->next = NULL;
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return fdt;
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out_arr:
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free_fdarr(fdt);
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out_fdt:
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kfree(fdt);
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out:
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return NULL;
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}
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/*
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* Expand the file descriptor table.
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* This function will allocate a new fdtable and both fd array and fdset, of
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* the given size.
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* Return <0 error code on error; 1 on successful completion.
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* The files->file_lock should be held on entry, and will be held on exit.
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*/
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static int expand_fdtable(struct files_struct *files, int nr)
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__releases(files->file_lock)
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__acquires(files->file_lock)
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{
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struct fdtable *new_fdt, *cur_fdt;
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spin_unlock(&files->file_lock);
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new_fdt = alloc_fdtable(nr);
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spin_lock(&files->file_lock);
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if (!new_fdt)
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return -ENOMEM;
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/*
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* extremely unlikely race - sysctl_nr_open decreased between the check in
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* caller and alloc_fdtable(). Cheaper to catch it here...
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*/
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if (unlikely(new_fdt->max_fds <= nr)) {
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free_fdarr(new_fdt);
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free_fdset(new_fdt);
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kfree(new_fdt);
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return -EMFILE;
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}
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/*
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* Check again since another task may have expanded the fd table while
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* we dropped the lock
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*/
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cur_fdt = files_fdtable(files);
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if (nr >= cur_fdt->max_fds) {
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/* Continue as planned */
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copy_fdtable(new_fdt, cur_fdt);
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rcu_assign_pointer(files->fdt, new_fdt);
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if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
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free_fdtable(cur_fdt);
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} else {
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/* Somebody else expanded, so undo our attempt */
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free_fdarr(new_fdt);
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free_fdset(new_fdt);
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kfree(new_fdt);
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}
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return 1;
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}
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/*
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* Expand files.
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* This function will expand the file structures, if the requested size exceeds
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* the current capacity and there is room for expansion.
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* Return <0 error code on error; 0 when nothing done; 1 when files were
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* expanded and execution may have blocked.
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* The files->file_lock should be held on entry, and will be held on exit.
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*/
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int expand_files(struct files_struct *files, int nr)
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{
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struct fdtable *fdt;
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fdt = files_fdtable(files);
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/*
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* N.B. For clone tasks sharing a files structure, this test
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* will limit the total number of files that can be opened.
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*/
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if (nr >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
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return -EMFILE;
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/* Do we need to expand? */
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if (nr < fdt->max_fds)
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return 0;
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/* Can we expand? */
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if (nr >= sysctl_nr_open)
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return -EMFILE;
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/* All good, so we try */
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return expand_fdtable(files, nr);
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}
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static int count_open_files(struct fdtable *fdt)
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{
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int size = fdt->max_fds;
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int i;
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/* Find the last open fd */
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for (i = size/(8*sizeof(long)); i > 0; ) {
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if (fdt->open_fds->fds_bits[--i])
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break;
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}
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i = (i+1) * 8 * sizeof(long);
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return i;
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}
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/*
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* Allocate a new files structure and copy contents from the
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* passed in files structure.
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* errorp will be valid only when the returned files_struct is NULL.
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*/
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struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
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{
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struct files_struct *newf;
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struct file **old_fds, **new_fds;
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int open_files, size, i;
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struct fdtable *old_fdt, *new_fdt;
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*errorp = -ENOMEM;
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newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
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if (!newf)
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goto out;
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atomic_set(&newf->count, 1);
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spin_lock_init(&newf->file_lock);
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newf->next_fd = 0;
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new_fdt = &newf->fdtab;
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new_fdt->max_fds = NR_OPEN_DEFAULT;
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new_fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init;
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new_fdt->open_fds = (fd_set *)&newf->open_fds_init;
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new_fdt->fd = &newf->fd_array[0];
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INIT_RCU_HEAD(&new_fdt->rcu);
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new_fdt->next = NULL;
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spin_lock(&oldf->file_lock);
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old_fdt = files_fdtable(oldf);
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open_files = count_open_files(old_fdt);
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/*
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* Check whether we need to allocate a larger fd array and fd set.
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*/
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while (unlikely(open_files > new_fdt->max_fds)) {
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spin_unlock(&oldf->file_lock);
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if (new_fdt != &newf->fdtab) {
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free_fdarr(new_fdt);
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free_fdset(new_fdt);
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kfree(new_fdt);
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}
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new_fdt = alloc_fdtable(open_files - 1);
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if (!new_fdt) {
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*errorp = -ENOMEM;
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goto out_release;
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}
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/* beyond sysctl_nr_open; nothing to do */
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if (unlikely(new_fdt->max_fds < open_files)) {
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free_fdarr(new_fdt);
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free_fdset(new_fdt);
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kfree(new_fdt);
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*errorp = -EMFILE;
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goto out_release;
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}
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/*
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* Reacquire the oldf lock and a pointer to its fd table
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* who knows it may have a new bigger fd table. We need
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* the latest pointer.
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*/
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spin_lock(&oldf->file_lock);
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old_fdt = files_fdtable(oldf);
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open_files = count_open_files(old_fdt);
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}
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old_fds = old_fdt->fd;
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new_fds = new_fdt->fd;
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memcpy(new_fdt->open_fds->fds_bits,
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old_fdt->open_fds->fds_bits, open_files/8);
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memcpy(new_fdt->close_on_exec->fds_bits,
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old_fdt->close_on_exec->fds_bits, open_files/8);
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for (i = open_files; i != 0; i--) {
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struct file *f = *old_fds++;
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if (f) {
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get_file(f);
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} else {
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/*
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* The fd may be claimed in the fd bitmap but not yet
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* instantiated in the files array if a sibling thread
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* is partway through open(). So make sure that this
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* fd is available to the new process.
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*/
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FD_CLR(open_files - i, new_fdt->open_fds);
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}
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rcu_assign_pointer(*new_fds++, f);
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}
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spin_unlock(&oldf->file_lock);
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/* compute the remainder to be cleared */
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size = (new_fdt->max_fds - open_files) * sizeof(struct file *);
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/* This is long word aligned thus could use a optimized version */
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memset(new_fds, 0, size);
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if (new_fdt->max_fds > open_files) {
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int left = (new_fdt->max_fds-open_files)/8;
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int start = open_files / (8 * sizeof(unsigned long));
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memset(&new_fdt->open_fds->fds_bits[start], 0, left);
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memset(&new_fdt->close_on_exec->fds_bits[start], 0, left);
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}
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rcu_assign_pointer(newf->fdt, new_fdt);
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return newf;
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out_release:
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kmem_cache_free(files_cachep, newf);
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out:
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return NULL;
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}
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static void __devinit fdtable_defer_list_init(int cpu)
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{
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struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
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spin_lock_init(&fddef->lock);
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INIT_WORK(&fddef->wq, free_fdtable_work);
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fddef->next = NULL;
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}
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void __init files_defer_init(void)
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{
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int i;
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for_each_possible_cpu(i)
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fdtable_defer_list_init(i);
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sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) &
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-BITS_PER_LONG;
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}
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struct files_struct init_files = {
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.count = ATOMIC_INIT(1),
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.fdt = &init_files.fdtab,
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.fdtab = {
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.max_fds = NR_OPEN_DEFAULT,
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.fd = &init_files.fd_array[0],
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.close_on_exec = (fd_set *)&init_files.close_on_exec_init,
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.open_fds = (fd_set *)&init_files.open_fds_init,
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.rcu = RCU_HEAD_INIT,
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},
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.file_lock = __SPIN_LOCK_UNLOCKED(init_task.file_lock),
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};
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/*
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* allocate a file descriptor, mark it busy.
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*/
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int alloc_fd(unsigned start, unsigned flags)
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{
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struct files_struct *files = current->files;
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unsigned int fd;
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int error;
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struct fdtable *fdt;
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spin_lock(&files->file_lock);
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repeat:
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fdt = files_fdtable(files);
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fd = start;
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if (fd < files->next_fd)
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fd = files->next_fd;
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if (fd < fdt->max_fds)
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fd = find_next_zero_bit(fdt->open_fds->fds_bits,
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fdt->max_fds, fd);
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error = expand_files(files, fd);
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if (error < 0)
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goto out;
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/*
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* If we needed to expand the fs array we
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* might have blocked - try again.
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*/
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if (error)
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goto repeat;
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if (start <= files->next_fd)
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files->next_fd = fd + 1;
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FD_SET(fd, fdt->open_fds);
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if (flags & O_CLOEXEC)
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FD_SET(fd, fdt->close_on_exec);
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else
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FD_CLR(fd, fdt->close_on_exec);
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error = fd;
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#if 1
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/* Sanity check */
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if (rcu_dereference(fdt->fd[fd]) != NULL) {
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printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
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rcu_assign_pointer(fdt->fd[fd], NULL);
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}
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#endif
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out:
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spin_unlock(&files->file_lock);
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return error;
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}
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int get_unused_fd(void)
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{
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return alloc_fd(0, 0);
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}
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EXPORT_SYMBOL(get_unused_fd);
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