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proc: Usable inode numbers for the namespace file descriptors.

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Assign a unique proc inode to each namespace, and use that
inode number to ensure we only allocate at most one proc
inode for every namespace in proc.

A single proc inode per namespace allows userspace to test
to see if two processes are in the same namespace.

This has been a long requested feature and only blocked because
a naive implementation would put the id in a global space and
would ultimately require having a namespace for the names of
namespaces, making migration and certain virtualization tricks
impossible.

We still don't have per superblock inode numbers for proc, which
appears necessary for application unaware checkpoint/restart and
migrations (if the application is using namespace file descriptors)
but that is now allowd by the design if it becomes important.

I have preallocated the ipc and uts initial proc inode numbers so
their structures can be statically initialized.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman
2011-06-15 10:21:48 -07:00
parent bf056bfa80
commit 98f842e675
18 changed files with 132 additions and 12 deletions
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14
fs/namespace.c
View File

@@ -2301,6 +2301,7 @@ dput_out:
static void free_mnt_ns(struct mnt_namespace *ns)
{
proc_free_inum(ns->proc_inum);
put_user_ns(ns->user_ns);
kfree(ns);
}
@@ -2317,10 +2318,16 @@ static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
{
struct mnt_namespace *new_ns;
int ret;
new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
if (!new_ns)
return ERR_PTR(-ENOMEM);
ret = proc_alloc_inum(&new_ns->proc_inum);
if (ret) {
kfree(new_ns);
return ERR_PTR(ret);
}
new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
atomic_set(&new_ns->count, 1);
new_ns->root = NULL;
@@ -2799,10 +2806,17 @@ static int mntns_install(struct nsproxy *nsproxy, void *ns)
return 0;
}
static unsigned int mntns_inum(void *ns)
{
struct mnt_namespace *mnt_ns = ns;
return mnt_ns->proc_inum;
}
const struct proc_ns_operations mntns_operations = {
.name = "mnt",
.type = CLONE_NEWNS,
.get = mntns_get,
.put = mntns_put,
.install = mntns_install,
.inum = mntns_inum,
};