[PATCH v3] erofs-utils: sort shared xattr

[Huang Jianan via Linux-erofs]

Sort shared xattr before writing to disk to ensure the consistency
of reproducible builds.

Signed-off-by: Huang Jianan <huangjia...@oppo.com>
---
since v2:
- Only traverse shared_xattrs_list once to clean up code.

since v1:
- Use strncmp instead of strcmp.

 lib/xattr.c | 42 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 36 insertions(+), 6 deletions(-)

diff --git a/lib/xattr.c b/lib/xattr.c
index 196133a..f6b2591 100644
--- a/lib/xattr.c
+++ b/lib/xattr.c
@@ -562,13 +562,31 @@ static struct erofs_bhops erofs_write_shared_xattrs_bhops 
= {
        .flush = erofs_bh_flush_write_shared_xattrs,
 };
 
+static int comp_xattr_item(const void *a, const void *b)
+{
+       const struct xattr_item *ia, *ib;
+       unsigned int la, lb;
+       int ret;
+
+       ia = (*((const struct inode_xattr_node **)a))->item;
+       ib = (*((const struct inode_xattr_node **)b))->item;
+       la = ia->len[0] + ia->len[1];
+       lb = ib->len[0] + ib->len[1];
+
+       ret = strncmp(ia->kvbuf, ib->kvbuf, min(la, lb));
+       if (ret != 0)
+               return ret;
+
+       return la > lb;
+}
+
 int erofs_build_shared_xattrs_from_path(const char *path)
 {
        int ret;
        struct erofs_buffer_head *bh;
-       struct inode_xattr_node *node, *n;
+       struct inode_xattr_node *node, *n, **sorted_n;
        char *buf;
-       unsigned int p;
+       unsigned int p, i;
        erofs_off_t off;
 
        /* check if xattr or shared xattr is disabled */
@@ -606,16 +624,26 @@ int erofs_build_shared_xattrs_from_path(const char *path)
        off %= EROFS_BLKSIZ;
        p = 0;
 
+       sorted_n = malloc(shared_xattrs_count * sizeof(n));
+       if (!sorted_n)
+               return -ENOMEM;
+       i = 0;
        list_for_each_entry_safe(node, n, &shared_xattrs_list, list) {
-               struct xattr_item *const item = node->item;
+               list_del(&node->list);
+               sorted_n[i++] = node;
+       }
+       DBG_BUGON(i != shared_xattrs_count);
+       qsort(sorted_n, shared_xattrs_count, sizeof(n), comp_xattr_item);
+
+       for (i = 0; i < shared_xattrs_count; i++) {
+               struct inode_xattr_node *const tnode = sorted_n[i];
+               struct xattr_item *const item = tnode->item;
                const struct erofs_xattr_entry entry = {
                        .e_name_index = item->prefix,
                        .e_name_len = item->len[0],
                        .e_value_size = cpu_to_le16(item->len[1])
                };
 
-               list_del(&node->list);
-
                item->shared_xattr_id = (off + p) /
                        sizeof(struct erofs_xattr_entry);
 
@@ -623,8 +651,10 @@ int erofs_build_shared_xattrs_from_path(const char *path)
                p += sizeof(struct erofs_xattr_entry);
                memcpy(buf + p, item->kvbuf, item->len[0] + item->len[1]);
                p = EROFS_XATTR_ALIGN(p + item->len[0] + item->len[1]);
-               free(node);
+               free(tnode);
        }
+
+       free(sorted_n);
        bh->fsprivate = buf;
        bh->op = &erofs_write_shared_xattrs_bhops;
 out:
-- 
2.25.1