[PATCH v2 1/3] init: Export name_to_dev_t and mark it const

[PATCH v2 1/3] init: Export name_to_dev_t and mark it const

[Dan Ehrenberg]

name_to_dev_t is useful in other pieces of code to initialize rootfs.
In the case of dm, the code is sometimes built in a module and other
times used to construct the rootfs; therefore it must be exported
as a symbol.

Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org>
---
 include/linux/mount.h | 2 +-
 init/do_mounts.c      | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/mount.h b/include/linux/mount.h
index c2c561d..bca086d 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -92,6 +92,6 @@ extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
 extern void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list);
 extern void mark_mounts_for_expiry(struct list_head *mounts);
 
-extern dev_t name_to_dev_t(char *name);
+extern dev_t name_to_dev_t(const char *name);
 
 #endif /* _LINUX_MOUNT_H */
diff --git a/init/do_mounts.c b/init/do_mounts.c
index eb41008..4b2daf1 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -207,7 +207,7 @@ done:
  *	bangs.
  */
 
-dev_t name_to_dev_t(char *name)
+dev_t name_to_dev_t(const char *name)
 {
 	char s[32];
 	char *p;
@@ -286,6 +286,7 @@ fail:
 done:
 	return res;
 }
+EXPORT_SYMBOL(name_to_dev_t);
 
 static int __init root_dev_setup(char *line)
 {
-- 
2.2.0.rc0.207.ga3a616c

[PATCH v2 2/3] init: Stricter checking of major:minor root= values

[Dan Ehrenberg]

In the kernel command-line, previously, root=1:2jakshflaksjdhfa would
be accepted and interpreted just like root=1:2. This patch adds
stricter checking so that additional characters after major:minor are
rejected by root=.

The goal of this patch is to help in unifying dm's interpretation of
its block device argument with the interpretation in other parts of
the kernel. dm rejects malformed major:minor pairs, and it seems
reasonable that root= could reject them as well.

Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org>
---
 init/do_mounts.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 4b2daf1..24f359f 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -226,8 +226,9 @@ dev_t name_to_dev_t(const char *name)
 
 	if (strncmp(name, "/dev/", 5) != 0) {
 		unsigned maj, min;
+		char dummy;
 
-		if (sscanf(name, "%u:%u", &maj, &min) == 2) {
+		if (sscanf(name, "%u:%u%c", &maj, &min, &dummy) == 2) {
 			res = MKDEV(maj, min);
 			if (maj != MAJOR(res) || min != MINOR(res))
 				goto fail;
-- 
2.2.0.rc0.207.ga3a616c

[PATCH v2 3/3] dm: Get devices using name_to_dev_t

[Dan Ehrenberg]

If a device is used as the root filesystem, it can't be built
off of devices which are within the root filesystem (just like
command line arguments to root=). For this reason, Linux has a
pseudo-filesystem for root= and md initialization based on the
function name_to_dev_t, which handles different ways of specifying
devices including PARTUUID and major:minor.

This patch applies name_to_dev_t to dm initialization. Rather
than assuming that all things which are not major:minor are paths
in an already-mounted filesystem, this patch first attempts
to look up the device in the filesystem, and applies name_to_dev_t
if it is not found there.

In terms of backwards compatibility, there are some cases where
behavior will be different:
- If you have a file in the current working directory named 1:2 and
  you initialze DM there, then it will try to use that file rather
  than the disk with that major/minor pair as a backing device.
- Similarly for other bdev types which name_to_dev_t knows how to
  interpret, the previous behavior was to repeatedly check for the
  existence of the file (e.g., while waiting for rootfs to come up)
  but the new behavior is to use the name_to_dev_t interpretation.
  For example, if you have a file named /dev/ubiblock0_0 which is
  a symlink to /dev/sda3, but it is not yet present when dm starts
  to initialize, then the name_to_dev_t interpretation will take
  precedence.
I believe these incompatibilities would only show up in really
strange setups with bad practices and we don't have to worry about
them.

Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org>
---
 drivers/md/dm-table.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 3afae9e..3ce1e01 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -18,6 +18,7 @@
 #include <linux/mutex.h>
 #include <linux/delay.h>
 #include <linux/atomic.h>
+#include <linux/mount.h>
 
 #define DM_MSG_PREFIX "table"
 
@@ -372,23 +373,18 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
 	int r;
 	dev_t uninitialized_var(dev);
 	struct dm_dev_internal *dd;
-	unsigned int major, minor;
 	struct dm_table *t = ti->table;
-	char dummy;
+	struct block_device *bdev;
 
 	BUG_ON(!t);
 
-	if (sscanf(path, "%u:%u%c", &major, &minor, &dummy) == 2) {
-		/* Extract the major/minor numbers */
-		dev = MKDEV(major, minor);
-		if (MAJOR(dev) != major || MINOR(dev) != minor)
-			return -EOVERFLOW;
+	/* convert the path to a device */
+	bdev = lookup_bdev(path);
+	if (IS_ERR(bdev)) {
+		dev = name_to_dev_t(path);
+		if (!dev)
+			return -ENODEV;
 	} else {
-		/* convert the path to a device */
-		struct block_device *bdev = lookup_bdev(path);
-
-		if (IS_ERR(bdev))
-			return PTR_ERR(bdev);
 		dev = bdev->bd_dev;
 		bdput(bdev);
 	}
-- 
2.2.0.rc0.207.ga3a616c

Re: [PATCH v2 1/3] init: Export name_to_dev_t and mark it const

[Mike Snitzer]

On Tue, Feb 10 2015 at  6:20pm -0500,
Dan Ehrenberg <dehrenberg@chromium.org> wrote:

> name_to_dev_t is useful in other pieces of code to initialize rootfs.
> In the case of dm, the code is sometimes built in a module and other
> times used to construct the rootfs; therefore it must be exported
> as a symbol.
> 
> Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org>

I'm going to pick these changes up and stage them in linux-dm.git's
'for-next' for Linux 4.1.

Al and/or others, if you have any objections to the simple
name_to_dev_t() changes in the first 2 patches of this set please
shout.

Thanks,
Mike

[PATCH v2 1/3] init: Export name_to_dev_t and mark it const

[Dan Ehrenberg]

name_to_dev_t is useful in other pieces of code to initialize rootfs.
In the case of dm, the code is sometimes built in a module and other
times used to construct the rootfs; therefore it must be exported
as a symbol.

Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org>
---
 include/linux/mount.h | 2 +-
 init/do_mounts.c      | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/mount.h b/include/linux/mount.h
index c2c561d..bca086d 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -92,6 +92,6 @@ extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
 extern void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list);
 extern void mark_mounts_for_expiry(struct list_head *mounts);
 
-extern dev_t name_to_dev_t(char *name);
+extern dev_t name_to_dev_t(const char *name);
 
 #endif /* _LINUX_MOUNT_H */
diff --git a/init/do_mounts.c b/init/do_mounts.c
index eb41008..4b2daf1 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -207,7 +207,7 @@ done:
  *	bangs.
  */
 
-dev_t name_to_dev_t(char *name)
+dev_t name_to_dev_t(const char *name)
 {
 	char s[32];
 	char *p;
@@ -286,6 +286,7 @@ fail:
 done:
 	return res;
 }
+EXPORT_SYMBOL(name_to_dev_t);
 
 static int __init root_dev_setup(char *line)
 {
-- 
2.2.0.rc0.207.ga3a616c