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[U-BOOT,3/3] btrfs: btfs_file_read: zero trailing data if no extent was found

Message ID 20230418-btrfs-extent-reads-v1-3-47ba9839f0cc@codewreck.org
State Superseded
Delegated to: Tom Rini
Headers show
Series btrfs: fix and improve read code | expand

Commit Message

Dominique Martinet April 18, 2023, 1:17 a.m. UTC 
From: Dominique Martinet <dominique.martinet@atmark-techno.com>

btfs_file_read's truncate path has a comment noting '>0 means no extent'
and bailing out immediately, but the buffer has not been written so
probably needs zeroing out.

This is a theorical fix only and hasn't been tested on a file that
actually runs this code path.

Signed-off-by: Dominique Martinet <dominique.martinet@atmark-techno.com>
---
 fs/btrfs/inode.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Comments

Dominique Martinet April 18, 2023, 2:43 a.m. UTC | #1 
Qu Wenruo wrote on Tue, Apr 18, 2023 at 10:04:56AM +0800:
> > This is a theorical fix only and hasn't been tested on a file that
> > actually runs this code path.
> 
> IIRC there is a memset() at the very beginning of btrfs_file_read() to set
> the whole dest memory to zero.

Right, sorry.

I'll drop this and send a new patch that removes the duplicate memset
(at "The whole file is a hole" comment) instead as seeing multiple
memsets is what made me think it'd be necessary without thinking; that
can be done even if we rework the function a bit in later cleanups...
diff mbox series

Patch

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index efffec0f2e68..23c006c98c3b 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -756,9 +756,12 @@  int btrfs_file_read(struct btrfs_root *root, u64 ino, u64 file_offset, u64 len,
 		btrfs_release_path(&path);
 		ret = lookup_data_extent(root, &path, ino, cur,
 					 &next_offset);
-		/* <0 is error, >0 means no extent */
-		if (ret)
+		/* <0 is error, >0 means no extent: zero end of buffer */
+		if (ret) {
+			if (ret > 0)
+				memset(dest + cur, 0, end - cur);
 			goto out;
+		}
 		fi = btrfs_item_ptr(path.nodes[0], path.slots[0],
 				    struct btrfs_file_extent_item);
 		ret = read_and_truncate_page(&path, fi, cur,