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SubjectRe: [PATCH] nfsd: enable UMH client tracker in container
24.04.2013 00:00, J. Bruce Fields пишет:
> On Fri, Apr 19, 2013 at 07:01:50AM -0700, Jeff Layton wrote:
>> On Tue, 16 Apr 2013 15:17:44 +0400
>> Stanislav Kinsbursky <skinsbursky@parallels.com> wrote:
>>
>>> This patch adds support for UserModeHelper tracker in a container.
>>> The reason for this is that the only containerised tracker ("nfsdcld") is
>>> going to be removed in 3.10 kernel, thus at least one more tracker have to be
>>> containerised to replace the deprecated one.
>>> UMH tracker looks more preferable comparing to legacy since it's the latest
>>> one.
>>> To make UMH tracker work in a container, we have to make sure, that it
>>> executes right binary (i.e., this binary have to be taken from the container
>>> environment).
>>> But, UMH is a kernel thread, which works in global root environment by design
>>> (kernel thread's root is inherited from kthreadd, which in turn inherited it's
>>> root from global init). So, the root have to be swapped to the container's
>>> one before binary execution.
>>>
>>> This patch passes "init" callback and private "data" to UMH interface, which
>>> are used to swap root for spawned kernel thread.
>>>
>>> Note: container's root can be stored on stack, because UMH calls are
>>> synchronous.
>>>
>>> Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
>>> ---
>>> fs/nfsd/nfs4recover.c | 29 ++++++++++++++++++++++-------
>>> 1 files changed, 22 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
>>> index 899ca26..15f8de6 100644
>>> --- a/fs/nfsd/nfs4recover.c
>>> +++ b/fs/nfsd/nfs4recover.c
>>> @@ -38,6 +38,7 @@
>>> #include <linux/crypto.h>
>>> #include <linux/sched.h>
>>> #include <linux/fs.h>
>>> +#include <linux/fs_struct.h>
>>> #include <linux/module.h>
>>> #include <net/net_namespace.h>
>>> #include <linux/sunrpc/rpc_pipe_fs.h>
>>> @@ -1122,12 +1123,28 @@ nfsd4_cltrack_legacy_recdir(const struct xdr_netobj *name)
>>> return result;
>>> }
>>>
>>> +static int nfsd_swap_root(struct subprocess_info *info, struct cred *new)
>>> +{
>>> + struct path *root = info->data;
>>> + struct fs_struct *fs = current->fs;
>>> + struct path current_root;
>>> +
>>> + spin_lock(&fs->lock);
>>> + current_root = fs->root;
>>> + fs->root = *root;
>>> + spin_unlock(&fs->lock);
>>> + if (current_root.dentry)
>>> + path_put(&current_root);
>>> + return 0;
>>> +}
>>> +
>>> static int
>>> nfsd4_umh_cltrack_upcall(char *cmd, char *arg, char *legacy)
>>> {
>>> char *envp[2];
>>> char *argv[4];
>>> int ret;
>>> + struct path root;
>>>
>>> if (unlikely(!cltrack_prog[0])) {
>>> dprintk("%s: cltrack_prog is disabled\n", __func__);
>>> @@ -1146,7 +1163,11 @@ nfsd4_umh_cltrack_upcall(char *cmd, char *arg, char *legacy)
>>> argv[2] = arg;
>>> argv[3] = NULL;
>>>
>>> - ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC);
>>> + get_fs_root(current->fs, &root);
>>> +
>>> + ret = call_usermodehelper_fns(argv[0], argv, envp, UMH_WAIT_PROC,
>>> + nfsd_swap_root, NULL, &root);
>>> +
>>> /*
>>> * Disable the upcall mechanism if we're getting an ENOENT or EACCES
>>> * error. The admin can re-enable it on the fly by using sysfs
>>> @@ -1185,12 +1206,6 @@ bin_to_hex_dup(const unsigned char *src, int srclen)
>>> static int
>>> nfsd4_umh_cltrack_init(struct net __attribute__((unused)) *net)
>>> {
>>> - /* XXX: The usermode helper s not working in container yet. */
>>> - if (net != &init_net) {
>>> - WARN(1, KERN_ERR "NFSD: attempt to initialize umh client "
>>> - "tracking in a container!\n");
>>> - return -EINVAL;
>>> - }
>>> return nfsd4_umh_cltrack_upcall("init", NULL, NULL);
>>> }
>>>
>>>
>>
>> I think this looks correct and like it'll work, but I wonder whether
>> we'd be best served by making this part of the UMH code itself?
>>
>> IOW, add some fields to the struct subprocess_info to hold the new
>> root, and then do what you're doing in nfsd_swap_root before calling
>> the "init" function?
>>
>> I imagine we'll eventually need do something similar for at least some
>> of the callers of call_usermodehelper so it would make sense to me to
>> not replicate copies of nfsd_swap_root all over the place.
>
> Agreed.
>

Hmm. Yes, me too.
Ok, I'll prepare patch for the UMH itself.
And resend.
Thanks, guys.

> --b.
>


--
Best regards,
Stanislav Kinsbursky
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