[PATCH] nbd: show nbd client pid in sysfs

Allow nbd to expose the nbd-client daemon's PID in /sys/block/nbd<x>/pid.

This is helpful for tracking connection status of a device and for
determining which nbd devices are currently in use.

Signed-off-by: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 17 insertions, 0 deletions

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 9d1035e8d9d8..7bf2cfbd6285 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -355,14 +355,30 @@ harderror:
         return NULL;
 }
 
+static ssize_t pid_show(struct gendisk *disk, char *page)
+{
+        return sprintf(page, "%ld\n",
+                (long) ((struct nbd_device *)disk->private_data)->pid);
+}
+
+static struct disk_attribute pid_attr = {
+        .attr = { .name = "pid", .mode = S_IRUGO },
+        .show = pid_show,
+};
+
 static void nbd_do_it(struct nbd_device *lo)
 {
         struct request *req;
 
         BUG_ON(lo->magic != LO_MAGIC);
 
+        lo->pid = current->pid;
+        sysfs_create_file(&lo->disk->kobj, &pid_attr.attr);
+
         while ((req = nbd_read_stat(lo)) != NULL)
                 nbd_end_request(req);
+
+        sysfs_remove_file(&lo->disk->kobj, &pid_attr.attr);
         return;
 }
 
diff --git a/include/linux/nbd.h b/include/linux/nbd.h
index d6b6dc09ad97..0f3e69302540 100644
--- a/include/linux/nbd.h
+++ b/include/linux/nbd.h
@@ -64,6 +64,7 @@ struct nbd_device {
         struct gendisk *disk;
         int blksize;
         u64 bytesize;
+        pid_t pid; /* pid of nbd-client, if attached */
 };
 
 #endif