Re: [PATCH V4 3/8] namespaces: expose ns instance serial numbers in proc

Andy Lutomirski
2014-08-21T21:13:28Z

On Aug 20, 2014 8:12 PM, "Richard Guy Briggs" <rgb-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>
> Expose the namespace instace serial numbers in the proc filesystem at
> /proc/<pid>/ns/<ns>_snum. The link text gives the serial number in hex.

What's the use case?

I understand the utility of giving unique numbers to the audit code,
but I don't think this part is necessary for that, and I'd like to
understand what else will use this before committing to a duplicative
API like this.

Note that this API is thoroughly incompatible with CRIU. If we do
this, someone will ask for a namespace number namespace, and that way
lies madness.

--Andy

>
> "snum" was chosen instead of "seq" for consistency with inum and there are a
> number of other uses of "seq" in the namespace code.
>
> Suggested-by: Serge E. Hallyn <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org>
> Signed-off-by: Richard Guy Briggs <rgb-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
> fs/proc/namespaces.c | 33 +++++++++++++++++++++++++--------
> 1 files changed, 25 insertions(+), 8 deletions(-)
>
> diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
> index 8902609..e953e0a 100644
> --- a/fs/proc/namespaces.c
> +++ b/fs/proc/namespaces.c
> @@ -47,12 +47,15 @@ static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
> struct inode *inode = dentry->d_inode;
> const struct proc_ns_operations *ns_ops = PROC_I(inode)->ns.ns_ops;
>
> - return dynamic_dname(dentry, buffer, buflen, "%s:[%lu]",
> - ns_ops->name, inode->i_ino);
> + if (strstr(dentry->d_iname, "_snum"))
> + return dynamic_dname(dentry, buffer, buflen, "%s_snum:[%llx]",
> + ns_ops->name, ns_ops->snum(PROC_I(inode)->ns.ns));
> + else
> + return dynamic_dname(dentry, buffer, buflen, "%s:[%lu]",
> + ns_ops->name, inode->i_ino);
> }
>
> -const struct dentry_operations ns_dentry_operations =
> -{
> +const struct dentry_operations ns_dentry_operations = {
> .d_delete = always_delete_dentry,
> .d_dname = ns_dname,
> };
> @@ -160,7 +163,10 @@ static int proc_ns_readlink(struct dentry *dentry, char __user *buffer, int bufl
> if (!ns)
> goto out_put_task;
>
> - snprintf(name, sizeof(name), "%s:[%u]", ns_ops->name, ns_ops->inum(ns));
> + if (strstr(dentry->d_iname, "_snum"))
> + snprintf(name, sizeof(name), "%s_snum:[%llx]", ns_ops->name, ns_ops->snum(ns));
> + else
> + snprintf(name, sizeof(name), "%s:[%u]", ns_ops->name, ns_ops->inum(ns));
> res = readlink_copy(buffer, buflen, name);
> ns_ops->put(ns);
> out_put_task:
> @@ -210,16 +216,23 @@ static int proc_ns_dir_readdir(struct file *file, struct dir_context *ctx)
>
> if (!dir_emit_dots(file, ctx))
> goto out;
> - if (ctx->pos >= 2 + ARRAY_SIZE(ns_entries))
> + if (ctx->pos >= 2 + 2 * ARRAY_SIZE(ns_entries))
> goto out;
> entry = ns_entries + (ctx->pos - 2);
> last = &ns_entries[ARRAY_SIZE(ns_entries) - 1];
> while (entry <= last) {
> const struct proc_ns_operations *ops = *entry;
> + char name[50];
> +
> if (!proc_fill_cache(file, ctx, ops->name, strlen(ops->name),
> proc_ns_instantiate, task, ops))
> break;
> ctx->pos++;
> + snprintf(name, sizeof(name), "%s_snum", ops->name);
> + if (!proc_fill_cache(file, ctx, name, strlen(name),
> + proc_ns_instantiate, task, ops))
> + break;
> + ctx->pos++;
> entry++;
> }
> out:
> @@ -247,9 +260,13 @@ static struct dentry *proc_ns_dir_lookup(struct inode *dir,
>
> last = &ns_entries[ARRAY_SIZE(ns_entries)];
> for (entry = ns_entries; entry < last; entry++) {
> - if (strlen((*entry)->name) != len)
> + char name[50];
> +
> + snprintf(name, sizeof(name), "%s_snum", (*entry)->name);
> + if (strlen((*entry)->name) != len && strlen(name) != len)
> continue;
> - if (!memcmp(dentry->d_name.name, (*entry)->name, len))
> + if (!memcmp(dentry->d_name.name, (*entry)->name, len)
> + || !memcmp(dentry->d_name.name, name, len))
> break;
> }
> if (entry == last)
> --
> 1.7.1
>
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