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]:36660 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753257Ab2LKONN convert rfc822-to-8bit (ORCPT ); Tue, 11 Dec 2012 09:13:13 -0500 Message-ID: <50C73F58.1080005@parallels.com> Date: Tue, 11 Dec 2012 18:12:40 +0400 From: Stanislav Kinsbursky MIME-Version: 1.0 To: "J. Bruce Fields" CC: , , Subject: Re: [Devel] [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> <50C73C60.8060405@parallels.com> In-Reply-To: <50C73C60.8060405@parallels.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Sender: linux-nfs-owner@vger.kernel.org List-ID: 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(...) { pth = d_path(&exp->ex_path, *bpp, *blen); } we can do something like this: void svc_export_request(...) { struct nfsd_net *nn = ... spin_lock(&dcache_lock); pth = __d_path(&exp->ex_path, &nn->root, *bpp, *blen); spin_unlock(&dcache_lock); } >> --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