LXR linux/fs/stack.c

   1#include <linux/module.h>
   2#include <linux/fs.h>
   3#include <linux/fs_stack.h>
   4
   5/* does _NOT_ require i_mutex to be held.
   6 *
   7 * This function cannot be inlined since i_size_{read,write} is rather
   8 * heavy-weight on 32-bit systems
   9 */
  10void fsstack_copy_inode_size(struct inode *dst, struct inode *src)
  11{
  12        loff_t i_size;
  13        blkcnt_t i_blocks;
  14
  15        /*
  16         * i_size_read() includes its own seqlocking and protection from
  17         * preemption (see include/linux/fs.h): we need nothing extra for
  18         * that here, and prefer to avoid nesting locks than attempt to keep
  19         * i_size and i_blocks in sync together.
  20         */
  21        i_size = i_size_read(src);
  22
  23        /*
  24         * But if CONFIG_LBDAF (on 32-bit), we ought to make an effort to
  25         * keep the two halves of i_blocks in sync despite SMP or PREEMPT -
  26         * though stat's generic_fillattr() doesn't bother, and we won't be
  27         * applying quotas (where i_blocks does become important) at the
  28         * upper level.
  29         *
  30         * We don't actually know what locking is used at the lower level;
  31         * but if it's a filesystem that supports quotas, it will be using
  32         * i_lock as in inode_add_bytes().  tmpfs uses other locking, and
  33         * its 32-bit is (just) able to exceed 2TB i_size with the aid of
  34         * holes; but its i_blocks cannot carry into the upper long without
  35         * almost 2TB swap - let's ignore that case.
  36         */
  37        if (sizeof(i_blocks) > sizeof(long))
  38                spin_lock(&src->i_lock);
  39        i_blocks = src->i_blocks;
  40        if (sizeof(i_blocks) > sizeof(long))
  41                spin_unlock(&src->i_lock);
  42
  43        /*
  44         * If CONFIG_SMP or CONFIG_PREEMPT on 32-bit, it's vital for
  45         * fsstack_copy_inode_size() to hold some lock around
  46         * i_size_write(), otherwise i_size_read() may spin forever (see
  47         * include/linux/fs.h).  We don't necessarily hold i_mutex when this
  48         * is called, so take i_lock for that case.
  49         *
  50         * And if CONFIG_LBADF (on 32-bit), continue our effort to keep the
  51         * two halves of i_blocks in sync despite SMP or PREEMPT: use i_lock
  52         * for that case too, and do both at once by combining the tests.
  53         *
  54         * There is none of this locking overhead in the 64-bit case.
  55         */
  56        if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
  57                spin_lock(&dst->i_lock);
  58        i_size_write(dst, i_size);
  59        dst->i_blocks = i_blocks;
  60        if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
  61                spin_unlock(&dst->i_lock);
  62}
  63EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);
  64
  65/* copy all attributes */
  66void fsstack_copy_attr_all(struct inode *dest, const struct inode *src)
  67{
  68        dest->i_mode = src->i_mode;
  69        dest->i_uid = src->i_uid;
  70        dest->i_gid = src->i_gid;
  71        dest->i_rdev = src->i_rdev;
  72        dest->i_atime = src->i_atime;
  73        dest->i_mtime = src->i_mtime;
  74        dest->i_ctime = src->i_ctime;
  75        dest->i_blkbits = src->i_blkbits;
  76        dest->i_flags = src->i_flags;
  77        dest->i_nlink = src->i_nlink;
  78}
  79EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);
  80