direct-io: allow direct writes to empty inodes

On a DIO_SKIP_HOLES filesystem, the ->get_block() method is currently
not allowed to create blocks for an empty inode.  This confusion comes
from trying to bit shift a negative number, so check the size of the
inode first.

The problem is most visible for hfsplus, because the fallback to
buffered I/O doesn't happen and the write fails with EIO.  This is in
part the fault of the module, because it gives a wrong return value on
->get_block(); that will be fixed in a separate patch.

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/direct-io.c b/fs/direct-io.c
index dbc1a1f080ceb231f0553ff270ee7663a5479bfd..ec2fb6fe6d37c628d5335b7a0971b464824b0623 100644 (file)
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -679,6 +679,7 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
        unsigned long fs_count; /* Number of filesystem-sized blocks */
        int create;
        unsigned int i_blkbits = sdio->blkbits + sdio->blkfactor;
+       loff_t i_size;
 
        /*
         * If there was a memory error and we've overwritten all the
@@ -708,8 +709,8 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
                 */
                create = dio->op == REQ_OP_WRITE;
                if (dio->flags & DIO_SKIP_HOLES) {
-                       if (fs_startblk <= ((i_size_read(dio->inode) - 1) >>
-                                                       i_blkbits))
+                       i_size = i_size_read(dio->inode);
+                       if (i_size && fs_startblk <= (i_size - 1) >> i_blkbits)
                                create = 0;
                }