So I think this is what we eventually need (thanks for the pointers you gave me!):
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 5a93a5db4fb0..e88ae4ce5263 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -2865,6 +2865,9 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
err = vfs_getattr(&path, &stat, STATX_BASIC_STATS, AT_STATX_SYNC_AS_STAT);
if (err)
goto out_nfserr;
+ if (! stat.result_mask & STATX_BTIME)
+ /* underlying FS does not offer btime so we can't share it */
+ bmval1 &= ~FATTR4_WORD1_TIME_CREATE;
if ((bmval0 & (FATTR4_WORD0_FILES_AVAIL | FATTR4_WORD0_FILES_FREE |
FATTR4_WORD0_FILES_TOTAL | FATTR4_WORD0_MAXNAME)) ||
(bmval1 & (FATTR4_WORD1_SPACE_AVAIL | FATTR4_WORD1_SPACE_FREE |
@@ -3265,6 +3268,14 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
p = xdr_encode_hyper(p, (s64)stat.mtime.tv_sec);
*p++ = cpu_to_be32(stat.mtime.tv_nsec);
}
+ /* support for btime here */
+ if (bmval1 & FATTR4_WORD1_TIME_CREATE) {
+ p = xdr_reserve_space(xdr, 12);
+ if (!p)
+ goto out_resource;
+ p = xdr_encode_hyper(p, (s64)stat.btime.tv_sec);
+ *p++ = cpu_to_be32(stat.btime.tv_nsec);
+ }
if (bmval1 & FATTR4_WORD1_MOUNTED_ON_FILEID) {
struct kstat parent_stat;
u64 ino = stat.ino;
diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
index 498e5a489826..5ef056ce7591 100644
--- a/fs/nfsd/nfsd.h
+++ b/fs/nfsd/nfsd.h
@@ -364,7 +364,7 @@ void nfsd_lockd_shutdown(void);
| FATTR4_WORD1_OWNER | FATTR4_WORD1_OWNER_GROUP | FATTR4_WORD1_RAWDEV \
| FATTR4_WORD1_SPACE_AVAIL | FATTR4_WORD1_SPACE_FREE | FATTR4_WORD1_SPACE_TOTAL \
| FATTR4_WORD1_SPACE_USED | FATTR4_WORD1_TIME_ACCESS | FATTR4_WORD1_TIME_ACCESS_SET \
- | FATTR4_WORD1_TIME_DELTA | FATTR4_WORD1_TIME_METADATA \
+ | FATTR4_WORD1_TIME_DELTA | FATTR4_WORD1_TIME_METADATA | FATTR4_WORD1_TIME_CREATE \
| FATTR4_WORD1_TIME_MODIFY | FATTR4_WORD1_TIME_MODIFY_SET | FATTR4_WORD1_MOUNTED_ON_FILEID)
#define NFSD4_SUPPORTED_ATTRS_WORD2 0
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