On Wed, Jan 28 2015 at 5:45pm -0500, Dan Ehrenberg <dehrenberg@xxxxxxxxxxxx> wrote: > 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@xxxxxxxxxxxx> > --- > 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); > } name_to_dev_t isn't an exported symbol so it is undefined if DM is built as a module (as many distros do). I was going to pick this up to submit via linux-dm.git but lost conviction once I hit compile errors and it became clear others need to weigh in on the broader use of name_to_dev_t(). Please Cc Al Viro on v2 (and any others that are returned by scripts/get_maintainer.pl). Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel