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SubjectRe: [Devel] [PATCH 2/6] nfsd: swap fs root in NFSd kthreads
11.12.2012 18:12, Stanislav Kinsbursky пишет:
> 11.12.2012 18:00, Stanislav Kinsbursky пишет:
>> 11.12.2012 00:28, J. Bruce Fields пишет:
>>> On Thu, Dec 06, 2012 at 06:34:47PM +0300, Stanislav Kinsbursky wrote:
>>>> NFSd does lookup. Lookup is done starting from current->fs->root.
>>>> NFSd is a kthread, cloned by kthreadd, and thus have global (but luckely
>>>> unshared) root.
>>>> So we have to swap root to those, which process, started NFSd, has. Because
>>>> that process can be in a container with it's own root.
>>>
>>> This doesn't sound right to me.
>>>
>>> Which lookups exactly do you see being done relative to
>>> current->fs->root ?
>>>
>>
>> Ok, you are right. I was mistaken here.
>> This is not a exactly lookup, but d_path() problem in svc_export_request().
>> I.e. without root swapping, d_path() will give not local export path (like "/export")
>> but something like this "/root/containers_root/export".
>>
>
> We, actually, can do it less in less aggressive way.
> I.e. instead root swap and current svc_export_request() implementation:
>
> void svc_export_request(...)
> {
> <snip>
> pth = d_path(&exp->ex_path, *bpp, *blen);
> <snip>
> }
>
> we can do something like this:
>
> void svc_export_request(...)
> {
> struct nfsd_net *nn = ...
> <snip>
> spin_lock(&dcache_lock);
> pth = __d_path(&exp->ex_path, &nn->root, *bpp, *blen);
> spin_unlock(&dcache_lock);
> <snip>
> }
>

No, this won't work. Sorry for noise.

>>> --b.
>>>
>>>>
>>>> Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
>>>> ---
>>>> fs/nfsd/netns.h | 1 +
>>>> fs/nfsd/nfssvc.c | 33 ++++++++++++++++++++++++++++++++-
>>>> 2 files changed, 33 insertions(+), 1 deletions(-)
>>>>
>>>> diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
>>>> index abfc97c..5c423c6 100644
>>>> --- a/fs/nfsd/netns.h
>>>> +++ b/fs/nfsd/netns.h
>>>> @@ -101,6 +101,7 @@ struct nfsd_net {
>>>> struct timeval nfssvc_boot;
>>>>
>>>> struct svc_serv *nfsd_serv;
>>>> + struct path root;
>>>> };
>>>>
>>>> extern int nfsd_net_id;
>>>> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
>>>> index cee62ab..177bb60 100644
>>>> --- a/fs/nfsd/nfssvc.c
>>>> +++ b/fs/nfsd/nfssvc.c
>>>> @@ -392,6 +392,7 @@ int nfsd_create_serv(struct net *net)
>>>>
>>>> set_max_drc();
>>>> do_gettimeofday(&nn->nfssvc_boot); /* record boot time */
>>>> + get_fs_root(current->fs, &nn->root);
>>>> return 0;
>>>> }
>>>>
>>>> @@ -426,8 +427,10 @@ void nfsd_destroy(struct net *net)
>>>> if (destroy)
>>>> svc_shutdown_net(nn->nfsd_serv, net);
>>>> svc_destroy(nn->nfsd_serv);
>>>> - if (destroy)
>>>> + if (destroy) {
>>>> + path_put(&nn->root);
>>>> nn->nfsd_serv = NULL;
>>>> + }
>>>> }
>>>>
>>>> int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
>>>> @@ -533,6 +536,25 @@ out:
>>>> return error;
>>>> }
>>>>
>>>> +/*
>>>> + * This function is actually slightly modified set_fs_root()<F9>
>>>> + */
>>>> +static void nfsd_swap_root(struct net *net)
>>>> +{
>>>> + struct nfsd_net *nn = net_generic(net, nfsd_net_id);
>>>> + struct fs_struct *fs = current->fs;
>>>> + struct path old_root;
>>>> +
>>>> + path_get(&nn->root);
>>>> + spin_lock(&fs->lock);
>>>> + write_seqcount_begin(&fs->seq);
>>>> + old_root = fs->root;
>>>> + fs->root = nn->root;
>>>> + write_seqcount_end(&fs->seq);
>>>> + spin_unlock(&fs->lock);
>>>> + if (old_root.dentry)
>>>> + path_put(&old_root);
>>>> +}
>>>>
>>>> /*
>>>> * This is the NFS server kernel thread
>>>> @@ -559,6 +581,15 @@ nfsd(void *vrqstp)
>>>> current->fs->umask = 0;
>>>>
>>>> /*
>>>> + * We have to swap NFSd kthread's fs->root.
>>>> + * Why so? Because NFSd can be started in container, which has it's own
>>>> + * root.
>>>> + * And so what? NFSd lookup files, and lookup start from
>>>> + * current->fs->root.
>>>> + */
>>>> + nfsd_swap_root(net);
>>>> +
>>>> + /*
>>>> * thread is spawned with all signals set to SIG_IGN, re-enable
>>>> * the ones that will bring down the thread
>>>> */
>>>>
>>
>>
>
>


--
Best regards,
Stanislav Kinsbursky
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