Messages in this thread | | | Date | Tue, 11 Dec 2012 18:51:35 +0400 | From | Stanislav Kinsbursky <> | Subject | Re: [Devel] [PATCH 2/6] nfsd: swap fs root in NFSd kthreads |
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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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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