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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 /fs/nfsd/nfsfh.h
parent35a30fc389b5961b42bb73ef751f3bc85190a118 (diff)
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>
Diffstat (limited to 'fs/nfsd/nfsfh.h')
-rw-r--r--fs/nfsd/nfsfh.h24
1 files changed, 23 insertions, 1 deletions
diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
index f84fe6bf9aee..e47cf6c2ac28 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;
}
}