From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: linux-nfs-owner@vger.kernel.org Received: from relay.parallels.com ([195.214.232.42]:34401 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752867Ab2LKOAx convert rfc822-to-8bit (ORCPT ); Tue, 11 Dec 2012 09:00:53 -0500 Message-ID: <50C73C60.8060405@parallels.com> Date: Tue, 11 Dec 2012 18:00:00 +0400 From: Stanislav Kinsbursky MIME-Version: 1.0 To: "J. Bruce Fields" CC: , , Subject: Re: [PATCH 2/6] nfsd: swap fs root in NFSd kthreads References: <20121206153204.30693.11408.stgit@localhost.localdomain> <20121206153447.30693.54128.stgit@localhost.localdomain> <20121210202842.GB17350@fieldses.org> In-Reply-To: <20121210202842.GB17350@fieldses.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Sender: linux-nfs-owner@vger.kernel.org List-ID: 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". > --b. > >> >> Signed-off-by: Stanislav Kinsbursky >> --- >> 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() >> + */ >> +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