[RFC PATCH v2 08/11] NFSD: avoid extra nfs4_acl passthru work unless needed

Mike Snitzer
2026-02-24T19:24:50Z

Avoid the nfsd4_decode_acl()'s memcpy() work, that
nfsd4_decode_nfs4_acl_passthru() requires, unless
nfsd4_encode_nfs4_acl_passthru() has already been called.

Implemented by enabling and checking a static_key.

Mike Snitzer <snitzer@hammerspace.com>
---
fs/nfsd/nfs4xdr.c | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 99db768ad97e..78941125eaef 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -287,6 +287,8 @@ nfsd4_decode_bitmap4(struct nfsd4_compoundargs *argp, u32 *bmval, u32 bmlen)
return status == -EBADMSG ? nfserr_bad_xdr : nfs_ok;
}

+static DEFINE_STATIC_KEY_FALSE(nfs4_acl_passthru);
+
__be32 nfsd4_decode_nfs4_acl_passthru(struct nfsd4_compoundargs *argp,
u32 *bmval, struct nfs4_acl **acl)
{
@@ -296,6 +298,9 @@ __be32 nfsd4_decode_nfs4_acl_passthru(struct nfsd4_compoundargs *argp,
__be32 status = nfs_ok;
void *p;

+ if (WARN_ON_ONCE(!static_key_enabled(&nfs4_acl_passthru.key)))
+ return nfserr_resource;
+
xdr_init_decode(&xdr, &(*acl)->payload,
(*acl)->payload.head[0].iov_base, NULL);

@@ -378,8 +383,8 @@ nfsd4_decode_acl(struct nfsd4_compoundargs *argp, struct nfs4_acl **acl,

if (!xdr_stream_subsegment(argp->xdr, &payload, acl_len))
return nfserr_bad_xdr;
- memcpy(&saved_payload, &payload, sizeof(struct xdr_buf));
-
+ if (static_key_enabled(&nfs4_acl_passthru.key))
+ memcpy(&saved_payload, &payload, sizeof(struct xdr_buf));
xdr_init_decode(&xdr, &payload, payload.head[0].iov_base, NULL);

if (xdr_stream_decode_u32(&xdr, &count) < 0) {
@@ -402,7 +407,9 @@ nfsd4_decode_acl(struct nfsd4_compoundargs *argp, struct nfs4_acl **acl,
status = nfserr_jukebox;
goto out;
}
- memcpy(&(*acl)->payload, &saved_payload, sizeof(struct xdr_buf));
+ if (static_key_enabled(&nfs4_acl_passthru.key))
+ memcpy(&(*acl)->payload, &saved_payload,
+ sizeof(struct xdr_buf));

(*acl)->naces = count;
for (ace = (*acl)->aces; ace < (*acl)->aces + count; ace++) {
@@ -3409,6 +3416,13 @@ static __be32 nfsd4_encode_nfs4_acl_passthru(struct xdr_stream *xdr,
uint32_t remaining = acl->len;
unsigned int npages = DIV_ROUND_UP(remaining, PAGE_SIZE);

+ /*
+ * GETACL will precede SETACL, if passthru is used for
+ * GETACL then enable SETACL's extra work required
+ * to support passthru.
+ */
+ static_key_enable(&nfs4_acl_passthru.key);
+
for (int i = 0; i < npages; i++) {
void *vaddr = page_address(acl->pages[i]);
size_t len = (remaining < PAGE_SIZE) ? remaining : PAGE_SIZE;
--
2.44.0