splice: implement default splice_read method

If f_op->splice_read() is not implemented, fall back to a plain read.
Use vfs_readv() to read into previously allocated pages.

This will allow splice and functions using splice, such as the loop
device, to work on all filesystems.  This includes "direct_io" files
in fuse which bypass the page cache.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 1 insertions, 10 deletions

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 9ca4bb014657..801f4ab83302 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -709,10 +709,6 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
         if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode))
                 goto out_putf;
 
-        /* new backing store needs to support loop (eg splice_read) */
-        if (!inode->i_fop->splice_read)
-                goto out_putf;
-
         /* size of the new backing store needs to be the same */
         if (get_loop_size(lo, file) != get_loop_size(lo, old_file))
                 goto out_putf;
@@ -788,12 +784,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
         error = -EINVAL;
         if (S_ISREG(inode->i_mode) || S_ISBLK(inode->i_mode)) {
                 const struct address_space_operations *aops = mapping->a_ops;
-                /*
-                 * If we can't read - sorry. If we only can't write - well,
-                 * it's going to be read-only.
-                 */
-                if (!file->f_op->splice_read)
-                        goto out_putf;
+
                 if (aops->write_begin)
                         lo_flags |= LO_FLAGS_USE_AOPS;
                 if (!(lo_flags & LO_FLAGS_USE_AOPS) && !file->f_op->write)