Re: [PATCH 2/2] erofs-utils: lib: refactor extended attribute name prefixes

[Gao Xiang]

On 2023/9/12 16:00, Jingbo Xu wrote:

Previously, when an extended attribute (xattr) name matches a long name
prefix, the attribute name after stripping the long name prefix is
cached in xattr_item.  This is somewhat different with those that don't
match any long name prefix or when long name prefixes feature is not
enabled, in which case the attribute name after stripping the predefined
short name prefix is cached in xattr_item.

The implementation described above makes it clumsy when stripping or
deleting specific attribute from one file, if the attribute name is in
the long name prefix format.

To fix this, for those attribute names that match the long name prefix,
make the attribute name with the predefined short name prefix stripped
cached in xattr_item just like normal attribute names.

To achieve this, add two new members `index` and `infix_len` to
xattr_item.  The semantics of the original `prefix` member is unchanged,
i.e. representing the index of the matched predefined short name prefix,
while `index` member represents the index of the long name prefix if
any, or it's the same as `prefix` otherwise.  The `infix_len` member
represents the length of the infix of the long name preifx if any, or 0
otherwise.

Signed-off-by: Jingbo Xu <jeffl...@linux.alibaba.com>
---
  lib/xattr.c | 253 +++++++++++++++++++---------------------------------
  1 file changed, 94 insertions(+), 159 deletions(-)

diff --git a/lib/xattr.c b/lib/xattr.c
index 54a6ae2..cac8db8 100644
--- a/lib/xattr.c
+++ b/lib/xattr.c
@@ -75,9 +75,9 @@
  struct xattr_item {
        struct xattr_item *next_shared_xattr;
        const char *kvbuf;
-       unsigned int hash[2], len[2], count;
+       unsigned int hash[2], len[2], count, infix_len;
        int shared_xattr_id;
-       u8 prefix;
+       u8 prefix, index;
        struct hlist_node node;
  };

@@ -115,9 +115,11 @@ static struct xattr_prefix { struct ea_type_node {

        struct list_head list;
-       struct xattr_prefix type;
-       u8 index;
+       u8 index, base_index;
+       const char *infix;
+       u8 infix_len;
  };
+
  static LIST_HEAD(ea_name_prefixes);
  static unsigned int ea_prefix_count;

@@ -154,7 +156,8 @@ static struct xattr_item *get_xattritem(u8 prefix, char *kvbuf,

                                        unsigned int len[2])

As discussed offline, I tend to drop u8 prefix here, and move match_prefix() in.

Thanks,
Gao Xiang