On 2/10/25 2:48 PM, Chuck Lever wrote: > On 2/3/25 10:03 PM, Gustavo A. R. Silva wrote: >> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are >> getting ready to enable it, globally. >> >> So, in order to avoid ending up with a flexible-array member in the >> middle of other structs, we use the `struct_group_tagged()` helper >> to create a new tagged `struct posix_acl_hdr`. This structure >> groups together all the members of the flexible `struct posix_acl` >> except the flexible array. >> >> As a result, the array is effectively separated from the rest of the >> members without modifying the memory layout of the flexible structure. >> We then change the type of the middle struct member currently causing >> trouble from `struct posix_acl` to `struct posix_acl_hdr`. >> >> We also want to ensure that when new members need to be added to the >> flexible structure, they are always included within the newly created >> tagged struct. For this, we use `static_assert()`. This ensures that the >> memory layout for both the flexible structure and the new tagged struct >> is the same after any changes. >> >> This approach avoids having to implement `struct posix_acl_hdr` as a >> completely separate structure, thus preventing having to maintain two >> independent but basically identical structures, closing the door to >> potential bugs in the future. >> >> We also use `container_of()` whenever we need to retrieve a pointer to >> the flexible structure, through which we can access the flexible-array >> member, if necessary. >> >> So, with these changes, fix the following warning: >> >> fs/nfs_common/nfsacl.c:45:26: warning: structure containing a flexible array >> member is not at the end of another structure >> [-Wflex-array-member-not-at-end] >> >> Signed-off-by: Gustavo A. R. Silva <[email protected]> >> --- >> fs/nfs_common/nfsacl.c | 8 +++++--- >> include/linux/posix_acl.h | 11 ++++++++--- >> 2 files changed, 13 insertions(+), 6 deletions(-) >> >> diff --git a/fs/nfs_common/nfsacl.c b/fs/nfs_common/nfsacl.c >> index ea382b75b26c..e2eaac14fd8e 100644 >> --- a/fs/nfs_common/nfsacl.c >> +++ b/fs/nfs_common/nfsacl.c >> @@ -42,7 +42,7 @@ struct nfsacl_encode_desc { >> }; >> >> struct nfsacl_simple_acl { >> - struct posix_acl acl; >> + struct posix_acl_hdr acl; >> struct posix_acl_entry ace[4]; >> }; >> >> @@ -112,7 +112,8 @@ int nfsacl_encode(struct xdr_buf *buf, unsigned int >> base, struct inode *inode, >> xdr_encode_word(buf, base, entries)) >> return -EINVAL; >> if (encode_entries && acl && acl->a_count == 3) { >> - struct posix_acl *acl2 = &aclbuf.acl; >> + struct posix_acl *acl2 = >> + container_of(&aclbuf.acl, struct posix_acl, hdr); >> >> /* Avoid the use of posix_acl_alloc(). nfsacl_encode() is >> * invoked in contexts where a memory allocation failure is >> @@ -177,7 +178,8 @@ bool nfs_stream_encode_acl(struct xdr_stream *xdr, >> struct inode *inode, >> return false; >> >> if (encode_entries && acl && acl->a_count == 3) { >> - struct posix_acl *acl2 = &aclbuf.acl; >> + struct posix_acl *acl2 = >> + container_of(&aclbuf.acl, struct posix_acl, hdr); >> >> /* Avoid the use of posix_acl_alloc(). nfsacl_encode() is >> * invoked in contexts where a memory allocation failure is >> diff --git a/include/linux/posix_acl.h b/include/linux/posix_acl.h >> index e2d47eb1a7f3..62d497763e25 100644 >> --- a/include/linux/posix_acl.h >> +++ b/include/linux/posix_acl.h >> @@ -27,11 +27,16 @@ struct posix_acl_entry { >> }; >> >> struct posix_acl { >> - refcount_t a_refcount; >> - unsigned int a_count; >> - struct rcu_head a_rcu; >> + /* New members MUST be added within the struct_group() macro below. */ >> + struct_group_tagged(posix_acl_hdr, hdr, >> + refcount_t a_refcount; >> + unsigned int a_count; >> + struct rcu_head a_rcu; >> + ); >> struct posix_acl_entry a_entries[] __counted_by(a_count); >> }; >> +static_assert(offsetof(struct posix_acl, a_entries) == sizeof(struct >> posix_acl_hdr), >> + "struct member likely outside of struct_group_tagged()"); >> >> #define FOREACH_ACL_ENTRY(pa, acl, pe) \ >> for(pa=(acl)->a_entries, pe=pa+(acl)->a_count; pa<pe; pa++) > > Trond, Anna - > > Let me know if I need to take this one via the NFSD tree. If not, > > Acked-by: Chuck Lever <[email protected]>
Gentle ping: Still waiting for a response. -- Chuck Lever
