On Sep 3, 2015, at 4:32 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> On Thu, Sep 03, 2015 at 04:00:11PM -0400, Jeff Layton wrote:
>> On Thu, 3 Sep 2015 15:42:55 -0400
>> "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
>>
>>> On Thu, Sep 03, 2015 at 03:05:48PM -0400, J. Bruce Fields wrote:
>>>> On Thu, Sep 03, 2015 at 02:45:44PM -0400, Jeff Layton wrote:
>>>>> On Thu, 3 Sep 2015 14:31:03 -0400
>>>>> "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
>>>>>
>>>>>> On Thu, Sep 03, 2015 at 01:36:25PM -0400, Jeff Layton wrote:
>>>>>>> This is the userland companion patch for the patch to add a "nowcc"
>>>>>>> option to knfsd. This just adds the necessary code to allow userspace
>>>>>>> to set that option.
>>>>>>>
>>>>>>> Signed-off-by: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
>>>>>>> ---
>>>>>>> support/include/nfs/export.h | 3 ++-
>>>>>>> support/nfs/exports.c | 5 +++++
>>>>>>> utils/exportfs/exportfs.c | 2 ++
>>>>>>> utils/exportfs/exports.man | 14 ++++++++++++++
>>>>>>> 4 files changed, 23 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/support/include/nfs/export.h b/support/include/nfs/export.h
>>>>>>> index 1194255899bd..68bee5c2f305 100644
>>>>>>> --- a/support/include/nfs/export.h
>>>>>>> +++ b/support/include/nfs/export.h
>>>>>>> @@ -26,7 +26,8 @@
>>>>>>> #define NFSEXP_CROSSMOUNT 0x4000
>>>>>>> #define NFSEXP_NOACL 0x8000 /* reserved for possible ACL related use */
>>>>>>> #define NFSEXP_V4ROOT 0x10000
>>>>>>> -#define NFSEXP_PNFS 0x20000
>>>>>>> +#define NFSEXP_PNFS 0x20000
>>>>>>> +#define NFSEXP_NOWCC 0x40000
>>>>>>> /*
>>>>>>> * All flags supported by the kernel before addition of the
>>>>>>> * export_features interface:
>>>>>>> diff --git a/support/nfs/exports.c b/support/nfs/exports.c
>>>>>>> index 0aea6f154f09..791b5f756c9c 100644
>>>>>>> --- a/support/nfs/exports.c
>>>>>>> +++ b/support/nfs/exports.c
>>>>>>> @@ -276,6 +276,7 @@ putexportent(struct exportent *ep)
>>>>>>> if (ep->e_flags & NFSEXP_NOREADDIRPLUS)
>>>>>>> fprintf(fp, "nordirplus,");
>>>>>>> fprintf(fp, "%spnfs,", (ep->e_flags & NFSEXP_PNFS)? "" : "no_");
>>>>>>> + fprintf(fp, "%swcc,", (ep->e_flags & NFSEXP_NOWCC) ? "no" : "");
>>>>>>> if (ep->e_flags & NFSEXP_FSID) {
>>>>>>> fprintf(fp, "fsid=%d,", ep->e_fsid);
>>>>>>> }
>>>>>>> @@ -586,6 +587,10 @@ parseopts(char *cp, struct exportent *ep, int warn, int *had_subtree_opt_ptr)
>>>>>>> setflags(NFSEXP_PNFS, active, ep);
>>>>>>> else if (!strcmp(opt, "no_pnfs"))
>>>>>>> clearflags(NFSEXP_PNFS, active, ep);
>>>>>>> + else if (!strcmp(opt, "wcc"))
>>>>>>> + clearflags(NFSEXP_NOWCC, active, ep);
>>>>>>> + else if (!strcmp(opt, "nowcc"))
>>>>>>> + setflags(NFSEXP_NOWCC, active, ep);
>>>>>>> else if (strncmp(opt, "anonuid=", 8) == 0) {
>>>>>>> char *oe;
>>>>>>> ep->e_anonuid = strtol(opt+8, &oe, 10);
>>>>>>> diff --git a/utils/exportfs/exportfs.c b/utils/exportfs/exportfs.c
>>>>>>> index 87582316b086..a2afc80ee6ea 100644
>>>>>>> --- a/utils/exportfs/exportfs.c
>>>>>>> +++ b/utils/exportfs/exportfs.c
>>>>>>> @@ -823,6 +823,8 @@ dump(int verbose, int export_format)
>>>>>>> c = dumpopt(c, "no_acl");
>>>>>>> if (ep->e_flags & NFSEXP_PNFS)
>>>>>>> c = dumpopt(c, "pnfs");
>>>>>>> + if (ep->e_flags & NFSEXP_NOWCC)
>>>>>>> + c = dumpopt(c, "nowcc");
>>>>>>> if (ep->e_flags & NFSEXP_FSID)
>>>>>>> c = dumpopt(c, "fsid=%d", ep->e_fsid);
>>>>>>> if (ep->e_uuid)
>>>>>>> diff --git a/utils/exportfs/exports.man b/utils/exportfs/exports.man
>>>>>>> index 93092463153b..9213a228bb04 100644
>>>>>>> --- a/utils/exportfs/exports.man
>>>>>>> +++ b/utils/exportfs/exports.man
>>>>>>> @@ -417,6 +417,20 @@ devices. The default can be explicitly requested with the
>>>>>>> .I no_pnfs
>>>>>>> option.
>>>>>>>
>>>>>>> +.TP
>>>>>>> +.IR nowcc
>>>>>>> +This option disables the collection and reporting of WCC (weak cache
>>>>>>> +consistency) data in NFSv3 requests. RFC 1813 recommends that all
>>>>>>> +servers report this information to the clients as it allows the client
>>>>>>> +to avoid some extra round trips to the server. In some underlying
>>>>>>> +filesystems however, collecting this data can be cost prohibitive and
>>>>>>> +atomicity is difficult to guarantee.
>>>
>>> By the way, independently of this change, maybe we should by default
>>> disable the pre-op attribute on distributed filesystems? As I
>>> understand it we're just depending on the i_mutex for atomicity, which
>>> can't be right in that case.
>>>
>>> --b.
>>
>> Right. In the case of something like a clustered or network filesystem
>> you really can't guarantee atomicity, so why even try?
>>
>> So, that is another option...we could add a flags field to the
>> export_operations struct and use one flag to indicate whether to send
>> wcc attrs. That'd give us the ability to add other flags in the future
>> as well.
>>
>> The reason I went with the export option is that I didn't really want
>> to add the flags field, and I figured the flexibility of being able to
>> do that on any filesystem might be helpful.
>>
>> That said, I'm open to doing it that way instead of (or in addition to)
>> the export option if you think it would be better.
>
> Well, it's sounding so far like:
>
> - nobody will want this on a non-distributed filesystem (hard to
> see what the benefit would be; and it might cost).
> - people probably *do* want this on any distributed filesystem.
> - we could save users some trouble by not giving them another
> export option which they might just set wrong.
Here's another vote for having the setting automatically
determined.
> Eh, but I think I'm wrong about #2. Dropping the pre-op attribute is
> arguably necessary for correctness, but dropping the post-op attribute
> as well isn't necessary and might hurt, right? OK.
--
Chuck Lever
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