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List:       busybox
Subject:    mountpoint
From:       Vladimir Dronnikov <dronnikov () gmail ! com>
Date:       2009-10-29 6:30:48
Message-ID: 6784529b0910282330y25f5e229ka1d4a4b1d08bfbb5 () mail ! gmail ! com
[Download RAW message or body]

Hello, Bernhard!

"mountpoint -n PATH" refuses to find out the name of mounted device in
case of so-called "anonymous superblock", e.g. for btrfs.
That is, reported st.st_rdev doesn't correspond to any block device under /dev

http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg02870.html

To outline the problem I prepared a patch (attached).
Please, comment, and may be fix.

Regards,
--
Vladimir

["test.patch" (application/octet-stream)]

--- busybox.orig/miscutils/mountpoint.c	Tue May  5 17:03:35 2009
+++ busybox/miscutils/mountpoint.c	Mon Oct 26 11:24:50 2009
@@ -55,8 +55,17 @@
 
 			if (opt & OPT_d)
 				printf("%u:%u\n", major(st_dev), minor(st_dev));
-			if (opt & OPT_n)
-				printf("%s %s\n", find_block_device(arg), arg);
+			if (opt & OPT_n) {
+				// get the name of mounted block device
+				char *d = find_block_device(arg);
+				// name is undefined, but device is mounted -> anonymous superblock!
+				if (NULL == d) {
+					d = (char *)"UNKNOWN";
+					// TODO: iterate /proc/mounts, or /proc/self/mountinfo
+					// to find out the device name
+				}
+				printf("%s %s\n", d, arg);
+			}
 			if (!(opt & (OPT_q | OPT_d | OPT_n)))
 				printf("%s is %sa mountpoint\n", arg, is_not_mnt ? "not " : "");
 			return is_not_mnt;


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