On 2020/9/8 上午6:35, Tom Rini wrote:
On Wed, Jun 24, 2020 at 06:03:11PM +0200, Marek Behún wrote:
From: Qu Wenruo wqu@suse.com
This version of btrfs_file_read() has the following new features:
- Tries all mirrors
- More handling on unaligned size
- Better compressed extent handling The old implementation doesn't handle compressed extent with offset properly: we need to read out the whole compressed extent, then decompress the whole extent, and only then copy the requested part.
Signed-off-by: Qu Wenruo wqu@suse.com Reviewed-by: Marek Behún marek.behun@nic.cz
Note that this introduces a warning with LLVM-10: fs/btrfs/btrfs.c:246:6: warning: variable 'real_size' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized] if (!len) { ^~~~ fs/btrfs/btrfs.c:255:12: note: uninitialized use occurs here if (len > real_size - offset) ^~~~~~~~~ fs/btrfs/btrfs.c:246:2: note: remove the 'if' if its condition is always true if (!len) { ^~~~~~~~~~ fs/btrfs/btrfs.c:228:18: note: initialize the variable 'real_size' to silence this warning loff_t real_size; ^ = 0 1 warning generated.
and I have silenced as suggested. I'm not 100% happy with that, but leave fixing it here and in upstream btrfs-progs to the btrfs-experts.
My bad. The warning is correct, and since the code is U-boot specific, it doesn't affect kernel (using page) nor btrfs-progs (not really do file read with offset).
The fix is a little complex.
In fact we need to always call btrfs_size() to grab the real_size, and then modify @len using real_size, either using real_size directly, or do some basic calculation.
BTW, I didn't see the btrfs rebuild work merged upstream. Is this planned or you just grab from some specific branch?
The proper fix would look like this:
diff --git a/fs/btrfs/btrfs.c b/fs/btrfs/btrfs.c index 786bb4733fbd..a1a7b3cf1afb 100644 --- a/fs/btrfs/btrfs.c +++ b/fs/btrfs/btrfs.c @@ -243,14 +243,13 @@ int btrfs_read(const char *file, void *buf, loff_t offset, loff_t len, return -EINVAL; }
- if (!len) { - ret = btrfs_size(file, &real_size); - if (ret < 0) { - error("Failed to get inode size: %s", file); - return ret; - } - len = real_size; + ret = btrfs_size(file, &real_size); + if (ret < 0) { + error("Failed to get inode size: %s", file); + return ret; } + if (!len) + len = real_size;
if (len > real_size - offset) len = real_size - offset;