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authorJ. Bruce Fields <bfields@redhat.com>2017-05-11 14:45:06 -0400
committerJ. Bruce Fields <bfields@redhat.com>2017-07-12 15:55:00 -0400
commit630458e730b82efe1f6eb90e6bcabad02fe76e20 (patch)
treea71f8715cbd69020f99cb9a5942b3ec16f4baefa
parent35a30fc389b5961b42bb73ef751f3bc85190a118 (diff)
downloadop-kernel-dev-630458e730b82efe1f6eb90e6bcabad02fe76e20.zip
op-kernel-dev-630458e730b82efe1f6eb90e6bcabad02fe76e20.tar.gz
nfsd4: factor ctime into change attribute
Factoring ctime into the nfsv4 change attribute gives us better properties than just i_version alone. Eventually we'll likely also expose this (as opposed to raw i_version) to userspace, at which point we'll want to move it to a common helper, called from either userspace or individual filesystems. For now, nfsd is the only user. Signed-off-by: J. Bruce Fields <bfields@redhat.com>
-rw-r--r--fs/nfsd/nfs3xdr.c2
-rw-r--r--fs/nfsd/nfs4xdr.c2
-rw-r--r--fs/nfsd/nfsfh.h24
3 files changed, 25 insertions, 3 deletions
diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
index b8838d3..bf444b6 100644
--- a/fs/nfsd/nfs3xdr.c
+++ b/fs/nfsd/nfs3xdr.c
@@ -260,7 +260,7 @@ void fill_post_wcc(struct svc_fh *fhp)
printk("nfsd: inode locked twice during operation.\n");
err = fh_getattr(fhp, &fhp->fh_post_attr);
- fhp->fh_post_change = d_inode(fhp->fh_dentry)->i_version;
+ fhp->fh_post_change = nfsd4_change_attribute(d_inode(fhp->fh_dentry));
if (err) {
fhp->fh_post_saved = false;
/* Grab the ctime anyway - set_change_info might use it */
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 54e212e..20fbcab 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -1973,7 +1973,7 @@ static __be32 *encode_change(__be32 *p, struct kstat *stat, struct inode *inode,
*p++ = cpu_to_be32(convert_to_wallclock(exp->cd->flush_time));
*p++ = 0;
} else if (IS_I_VERSION(inode)) {
- p = xdr_encode_hyper(p, inode->i_version);
+ p = xdr_encode_hyper(p, nfsd4_change_attribute(inode));
} else {
*p++ = cpu_to_be32(stat->ctime.tv_sec);
*p++ = cpu_to_be32(stat->ctime.tv_nsec);
diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
index f84fe6b..e47cf6c 100644
--- a/fs/nfsd/nfsfh.h
+++ b/fs/nfsd/nfsfh.h
@@ -241,6 +241,28 @@ fh_clear_wcc(struct svc_fh *fhp)
}
/*
+ * We could use i_version alone as the change attribute. However,
+ * i_version can go backwards after a reboot. On its own that doesn't
+ * necessarily cause a problem, but if i_version goes backwards and then
+ * is incremented again it could reuse a value that was previously used
+ * before boot, and a client who queried the two values might
+ * incorrectly assume nothing changed.
+ *
+ * By using both ctime and the i_version counter we guarantee that as
+ * long as time doesn't go backwards we never reuse an old value.
+ */
+static inline u64 nfsd4_change_attribute(struct inode *inode)
+{
+ u64 chattr;
+
+ chattr = inode->i_ctime.tv_sec;
+ chattr <<= 30;
+ chattr += inode->i_ctime.tv_nsec;
+ chattr += inode->i_version;
+ return chattr;
+}
+
+/*
* Fill in the pre_op attr for the wcc data
*/
static inline void
@@ -253,7 +275,7 @@ fill_pre_wcc(struct svc_fh *fhp)
fhp->fh_pre_mtime = inode->i_mtime;
fhp->fh_pre_ctime = inode->i_ctime;
fhp->fh_pre_size = inode->i_size;
- fhp->fh_pre_change = inode->i_version;
+ fhp->fh_pre_change = nfsd4_change_attribute(inode);
fhp->fh_pre_saved = true;
}
}
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