stack.c

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#include <linux/export.h>
#include <linux/fs.h>
#include <linux/fs_stack.h>

/* does _NOT_ require i_mutex to be held.
 *
 * This function cannot be inlined since i_size_{read,write} is rather
 * heavy-weight on 32-bit systems
 */
void fsstack_copy_inode_size(struct inode *dst, struct inode *src)
{
    loff_t i_size;
    blkcnt_t i_blocks;

    /*
     * i_size_read() includes its own seqlocking and protection from
     * preemption (see include/linux/fs.h): we need nothing extra for
     * that here, and prefer to avoid nesting locks than attempt to keep
     * i_size and i_blocks in sync together.
     */
    i_size = i_size_read(src);

    /*
     * But if CONFIG_LBDAF (on 32-bit), we ought to make an effort to
     * keep the two halves of i_blocks in sync despite SMP or PREEMPT -
     * though stat's generic_fillattr() doesn't bother, and we won't be
     * applying quotas (where i_blocks does become important) at the
     * upper level.
     *
     * We don't actually know what locking is used at the lower level;
     * but if it's a filesystem that supports quotas, it will be using
     * i_lock as in inode_add_bytes().
     */
    if (sizeof(i_blocks) > sizeof(long))
        spin_lock(&src->i_lock);
    i_blocks = src->i_blocks;
    if (sizeof(i_blocks) > sizeof(long))
        spin_unlock(&src->i_lock);

    /*
     * If CONFIG_SMP or CONFIG_PREEMPT on 32-bit, it's vital for
     * fsstack_copy_inode_size() to hold some lock around
     * i_size_write(), otherwise i_size_read() may spin forever (see
     * include/linux/fs.h).  We don't necessarily hold i_mutex when this
     * is called, so take i_lock for that case.
     *
     * And if CONFIG_LBADF (on 32-bit), continue our effort to keep the
     * two halves of i_blocks in sync despite SMP or PREEMPT: use i_lock
     * for that case too, and do both at once by combining the tests.
     *
     * There is none of this locking overhead in the 64-bit case.
     */
    if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
        spin_lock(&dst->i_lock);
    i_size_write(dst, i_size);
    dst->i_blocks = i_blocks;
    if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
        spin_unlock(&dst->i_lock);
}
EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);

/* copy all attributes */
void fsstack_copy_attr_all(struct inode *dest, const struct inode *src)
{
    dest->i_mode = src->i_mode;
    dest->i_uid = src->i_uid;
    dest->i_gid = src->i_gid;
    dest->i_rdev = src->i_rdev;
    dest->i_atime = src->i_atime;
    dest->i_mtime = src->i_mtime;
    dest->i_ctime = src->i_ctime;
    dest->i_blkbits = src->i_blkbits;
    dest->i_flags = src->i_flags;
    set_nlink(dest, src->i_nlink);
}
EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);