[BUG] When testing with unaligned read, if a specific length is passed in, btrfs driver will read out nothing:
=> load host 0 $kernel_addr_r 5k_file 0x1000 0 0 bytes read in 0 ms But if no length is passed in, it works fine, even if we pass a non-zero length: => load host 0 $kernel_addr_r 5k_file 0 0x1000 1024 bytes read in 0 ms [CAUSE] In btrfs_read() if we have a larger size than our file, we will try to truncate it using the file size. However the real file size is not initialized if @len is not zero, thus we always truncate our length to 0, and cause the problem. [FIX] Fix it by just always do the file size check. In fact btrfs_size() always follow soft link, thus it will return the real file size correctly. Signed-off-by: Qu Wenruo <w...@suse.com> --- fs/btrfs/btrfs.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/fs/btrfs/btrfs.c b/fs/btrfs/btrfs.c index 4cdbbbe3d066..309cd595d37d 100644 --- a/fs/btrfs/btrfs.c +++ b/fs/btrfs/btrfs.c @@ -246,16 +246,17 @@ 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 > real_size - offset) + /* + * If the length is 0 (meaning read the whole file) or the range is + * beyond file size, truncate it to the end of the file. + */ + if (!len || len > real_size - offset) len = real_size - offset; ret = btrfs_file_read(root, ino, offset, len, buf); -- 2.37.1