fs: btrfs: fix the false alert of decompression failure

There are some cases where decompressed sectors can have padding zeros.

In kernel code, we have lines to address such situation:

        /*
         * btrfs_getblock is doing a zero on the tail of the page too,
         * but this will cover anything missing from the decompressed
         * data.
         */
        if (bytes < destlen)
                memset(kaddr+bytes, 0, destlen-bytes);
        kunmap_local(kaddr);

But not in U-boot code, thus we have some reports of U-boot failed to
read compressed files in btrfs.

Fix it by doing the same thing of the kernel, for both inline and
regular compressed extents.

Reported-by: Matwey Kornilov <matwey.kornilov@gmail.com>
Link: https://bugzilla.suse.com/show_bug.cgi?id=1183717


Fixes: a26a6bed ("fs: btrfs: Introduce btrfs_read_extent_inline() and btrfs_read_extent_reg()")
Signed-off-by: Qu Wenruo <wqu@suse.com>

fs/btrfs/inode.c

@@ -390,10 +390,16 @@ int btrfs_read_extent_inline(struct btrfs_path *path,
 			   csize);
 	ret = btrfs_decompress(btrfs_file_extent_compression(leaf, fi),
 			       cbuf, csize, dbuf, dsize);
-	if (ret < 0 || ret != dsize) {
+	if (ret == (u32)-1) {
 		ret = -EIO;
 		goto out;
 	}
+	/*
+	 * The compressed part ends before sector boundary, the remaining needs
+	 * to be zeroed out.
+	 */
+	if (ret < dsize)
+		memset(dbuf + ret, 0, dsize - ret);
 	memcpy(dest, dbuf, dsize);
 	ret = dsize;
 out:
@@ -494,10 +500,16 @@ int btrfs_read_extent_reg(struct btrfs_path *path,
 
 	ret = btrfs_decompress(btrfs_file_extent_compression(leaf, fi), cbuf,
 			       csize, dbuf, dsize);
-	if (ret != dsize) {
+	if (ret == (u32)-1) {
 		ret = -EIO;
 		goto out;
 	}
+	/*
+	 * The compressed part ends before sector boundary, the remaining needs
+	 * to be zeroed out.
+	 */
+	if (ret < dsize)
+		memset(dbuf + ret, 0, dsize - ret);
 	/* Then copy the needed part */
 	memcpy(dest, dbuf + btrfs_file_extent_offset(leaf, fi), len);
 	ret = len;