[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 wqu@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 741c6e20f533..9145727058d4 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);