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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>
This commit is contained in:
J. Bruce Fields 2017-05-11 14:45:06 -04:00
parent 35a30fc389
commit 630458e730
3 changed files with 25 additions and 3 deletions
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2
fs/nfsd/nfs3xdr.c
View File

@ -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 */

2
fs/nfsd/nfs4xdr.c
View File

@ -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);

24
fs/nfsd/nfsfh.h
View File

@ -240,6 +240,28 @@ fh_clear_wcc(struct svc_fh *fhp)
fhp->fh_pre_saved = false;
}
/*
* 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
*/
@ -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;
}
}