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 <[email protected]> >> >> 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 <[email protected]> >> Reviewed-by: Marek Behún <[email protected]> > > 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;
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