Date: Fri, 14 Apr 2017 22:44:53 +0000 From: Rick Macklem <rmacklem@uoguelph.ca> To: "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org> Cc: "jim@ks.uiuc.edu" <jim@ks.uiuc.edu> Subject: NFSv4 Linux client atime for exclusive create Message-ID: <YTXPR01MB018992D6CDD2A578B4AC946BDD050@YTXPR01MB0189.CANPRD01.PROD.OUTLOOK.COM>
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PR#218218 reports a problem where a file created by an NFSv4 mount (using a=
recent
Linux kernel) results in a bogus atime for the newly created file.
With the help of a packet trace from the problem reported I now know what i=
s
happening, but it turns out to be interesting and I am not sure I have a go=
od way
to fix it.
Here's the story...
- The Linux client does an Exclusive create.
- As was the norm for NFSv3, the FreeBSD server stores the create_verifier =
for this
exclusive create in the atime field of the newly created file, so it can =
be checked
for a retry of the exclusive create.
--> For NFSv3, it was required that a client follow an exclusive create w=
ith a Setattr
of atime to fix the atime.
It turns out that, for NFSv4, the client is not required to do the Setattr =
of atime.
(The FreeBSD client does do this and I think older Linux NFSv4 clients did.=
)
--> This Linux client follows the exclusive create with a Setattr, but only=
for the "mode"
attribute, leaving the create_verifier in the atime field.
I can think of two ways to fix this:
1 - Make the Setattr set atime whenever it sets any other attribute.
--> This would result in atime being set for changes to the file's met=
adata, which is not
what atime is supposed to do. (Yuck!)
2 - For NFSv4, store the create_verifier in an extended attribute instead o=
f atime.
--> I think this would work, but it would imply that only file systems=
that support
extended attributes (UFS, ZFS, ??) could be exported to NFSv4 cl=
ients.
Anyone have other ideas w.r.t. how to fix this?
Does restricting NFSv4 exports to file systems that support extended attrib=
utes sound
reasonable?
Thanks for any comments w.r.t. this, rick=
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