Merge tag 'erofs-for-6.6-rc5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs

Pull erofs fixes from Gao Xiang:

 - Fix a memory leak issue when using LZMA global compressed
   deduplication

 - Fix empty device tags in flatdev mode

 - Update documentation for recent new features

* tag 'erofs-for-6.6-rc5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs:
  erofs: update documentation
  erofs: allow empty device tags in flatdev mode
  erofs: fix memory leak of LZMA global compressed deduplication

Documentation/filesystems/erofs.rst

@@ -58,12 +58,14 @@ Here are the main features of EROFS:
 
  - Support extended attributes as an option;
 
+ - Support a bloom filter that speeds up negative extended attribute lookups;
+
  - Support POSIX.1e ACLs by using extended attributes;
 
  - Support transparent data compression as an option:
-   LZ4 and MicroLZMA algorithms can be used on a per-file basis; In addition,
-   inplace decompression is also supported to avoid bounce compressed buffers
-   and page cache thrashing.
+   LZ4, MicroLZMA and DEFLATE algorithms can be used on a per-file basis; In
+   addition, inplace decompression is also supported to avoid bounce compressed
+   buffers and unnecessary page cache thrashing.
 
  - Support chunk-based data deduplication and rolling-hash compressed data
    deduplication;
@@ -268,6 +270,38 @@ details.)
 
 By the way, chunk-based files are all uncompressed for now.
 
+Long extended attribute name prefixes
+-------------------------------------
+There are use cases where extended attributes with different values can have
+only a few common prefixes (such as overlayfs xattrs).  The predefined prefixes
+work inefficiently in both image size and runtime performance in such cases.
+
+The long xattr name prefixes feature is introduced to address this issue.  The
+overall idea is that, apart from the existing predefined prefixes, the xattr
+entry could also refer to user-specified long xattr name prefixes, e.g.
+"trusted.overlay.".
+
+When referring to a long xattr name prefix, the highest bit (bit 7) of
+erofs_xattr_entry.e_name_index is set, while the lower bits (bit 0-6) as a whole
+represent the index of the referred long name prefix among all long name
+prefixes.  Therefore, only the trailing part of the name apart from the long
+xattr name prefix is stored in erofs_xattr_entry.e_name, which could be empty if
+the full xattr name matches exactly as its long xattr name prefix.
+
+All long xattr prefixes are stored one by one in the packed inode as long as
+the packed inode is valid, or in the meta inode otherwise.  The
+xattr_prefix_count (of the on-disk superblock) indicates the total number of
+long xattr name prefixes, while (xattr_prefix_start * 4) indicates the start
+offset of long name prefixes in the packed/meta inode.  Note that, long extended
+attribute name prefixes are disabled if xattr_prefix_count is 0.
+
+Each long name prefix is stored in the format: ALIGN({__le16 len, data}, 4),
+where len represents the total size of the data part.  The data part is actually
+represented by 'struct erofs_xattr_long_prefix', where base_index represents the
+index of the predefined xattr name prefix, e.g. EROFS_XATTR_INDEX_TRUSTED for
+"trusted.overlay." long name prefix, while the infix string keeps the string
+after stripping the short prefix, e.g. "overlay." for the example above.
+
 Data compression
 ----------------
 EROFS implements fixed-sized output compression which generates fixed-sized

fs/erofs/decompressor_lzma.c

@@ -217,9 +217,12 @@ int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
 			strm->buf.out_size = min_t(u32, outlen,
 						   PAGE_SIZE - pageofs);
 			outlen -= strm->buf.out_size;
-			if (!rq->out[no] && rq->fillgaps)	/* deduped */
+			if (!rq->out[no] && rq->fillgaps) {	/* deduped */
 				rq->out[no] = erofs_allocpage(pagepool,
 						GFP_KERNEL | __GFP_NOFAIL);
+				set_page_private(rq->out[no],
+						 Z_EROFS_SHORTLIVED_PAGE);
+			}
 			if (rq->out[no])
 				strm->buf.out = kmap(rq->out[no]) + pageofs;
 			pageofs = 0;

fs/erofs/super.c

@@ -235,7 +235,7 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
 		return PTR_ERR(ptr);
 	dis = ptr + erofs_blkoff(sb, *pos);
 
-	if (!dif->path) {
+	if (!sbi->devs->flatdev && !dif->path) {
 		if (!dis->tag[0]) {
 			erofs_err(sb, "empty device tag @ pos %llu", *pos);
 			return -EINVAL;