[Lustre-discuss] problem with too many (default) ACLs on a directory

[Andreas Dilger]

On 2010-05-12, at 06:15, Frederik Ferner wrote:
> we are having problems with ACLs at the moment. As far as we understand
> this is what has happened.
> 
> We have a directory with 33 default ACLs on it in addition to 32 other ACLs.
> 
> Our problem started when a user created a subdirectory in the directory
> with the 33 default ACLs. This worked but the new directory now is
> inaccessible. The number of ACLs on the initial directory does not seem
> to matter.

For a long time there was a kernel limit of 32 ACLs on a single file.  Looking at newer kernel code it seems this limit is not longer present (it just tries to store the maximum xattr size possible to hold the ACL).

I see in the Lustre code that we have some constants still related to this:

# define LUSTRE_POSIX_ACL_MAX_ENTRIES   (32)
#  define LUSTRE_POSIX_ACL_MAX_SIZE      \
                (mds_xattr_acl_size(LUSTRE_POSIX_ACL_MAX_ENTRIES))

It does seem that the MDS should prevent storing an xattr that is larger than this size, but it is possible that if you are building the ACL incrementally it misses this limit check.  It may very well be that by creating a default ACL will bypass this limit and then when it is inherited by the new directory it breaks...

The relevant code is:

int mds_setxattr_internal(struct ptlrpc_request *req, struct mds_body *body)
{
        /* currently lustre limit xattr size */
        if (body->valid & OBD_MD_FLXATTR &&
            !strcmp(xattr_name, XATTR_NAME_ACL_ACCESS)) {
                xattrlen = lustre_msg_buflen(req->rq_reqmsg,
                                             REQ_REC_OFF + 2);

                if (xattrlen > LUSTRE_POSIX_ACL_MAX_SIZE)
                        GOTO(out, -ERANGE);
        }

but it should also check if the xattr_name is XATTR_NAME_ACL_DEFAULT.

        if (body->valid & OBD_MD_FLXATTR &&
            (!strcmp(xattr_name, XATTR_NAME_ACL_ACCESS) ||
             !strcmp(xattr_name, XATTR_NAME_ACL_DEFAULT)) {

Having a fixed maximum number of ACLs is important for Lustre, since the RDMA reply buffers have to be allocated before the client knows how many ACLs are stored on the file.

Cheers, Andreas
--
Andreas Dilger
Lustre Technical Lead
Oracle Corporation Canada Inc.