On Wed, 22 Mar 2023, Xiao Ni wrote: > On Tue, Mar 14, 2023 at 8:08 AM NeilBrown <neilb@xxxxxxx> wrote: > > > > > > mdopen() will use create_named_array() to ask the kernel to create the > > given md array, but only if it is given a number or name. > > If it is NOT given a name and is required to choose one itself using > > find_free_devnm() it does NOT use create_named_array(). > > > > On kernels with CONFIG_BLOCK_LEGACY_AUTOLOAD not set, this can result in > > failure to assemble an array. This can particularly seen when the > > "name" of the array begins with a host name different to the name of the > > host running the command. > > > > So add the missing call to create_named_array(). > > > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=217074 > > Hi Neil > > I have two questions, hope you can help to understand the function > create_mddev better. > > Frist, from the comment7 of the bug you mentioned: > > There are two different sorts names. Note that you almost > acknowledged this by writing "name for my md device node" while the > documentation only talks about names for "md devices", not for "md > device nodes". > > There are > 1/ there are names in /dev or /dev/md/ (device nodes) > 2/ there are names that appear in /proc/mdstat and in /sys/block/ (devices) > > Thanks for the clarification. But it looks like it doesn't work like > what you said. > For example: > mdadm -CR /dev/md/root -l0 -n2 /dev/sda /dev/sdc --name=test > cat /proc/mdstat > Personalities : [raid0] > md127 : active raid0 sdc[1] sda[0] > 3906764800 blocks super 1.2 512k chunks > cd /sys/block/md127/md/ > > In /proc/mdstat and /sys/block, they all use md127 rather than the name(root) Try again with "CREATE names=yes" in /etc/mdadm.conf. mdadm generally tries to keep: - the names in /dev/ - the names in /dev/md/ - the names in /proc/mdstat - the names stored in the metadata in sync. It can only do this when: - you enabled "names=yes" - you don't confuse it by specifying a device name (/dev/md/root) that is different from the metadata names "test". If you don't have "names=yes" then the name in /proc/mdstat and the name in /dev/md* will be numeric. The name in /dev/md/ and the name in the metadata can be different and will usually be the same. If you explicitly give a different name with --name= than the device name then obviously they will be different. If you then stop the array and restart with "mdadm -As" or "mdadm -I /dev/sda; mdadm -I /dev/sdb" then mdadm will create a name in /dev/md/ that matches the name in the metadata. > > Before this patch, it creates a symbol link with the name root rather than test > ll /dev/md/root > lrwxrwxrwx. 1 root root 8 Mar 21 22:35 /dev/md/root -> ../md127 That is what you asked it to do. > > So "test" which is specified by --name looks like it has little usage. > It is stored in the metadata. You can see it in --examine output. If you reassemble the array without specifying a device name, it will use the name "test". > > By the way, after this patch, the symbol link /dev/md/root can't be > created anymore. > Is it a regression problem? I cannot reproduce any problem like that. Please provide a sequence of steps so that I can try to duplicate it. > > Second, are there possibilities that the arguments "dev" and "name" of > function create_mddev > are null at the same time? No. For Build or Create, dev is never NULL. For Assemble and Incremental, name is never NULL. > After some tests, I found dev can't be null when creating a raid > device. It can be checked before > calling create_mddev. And we must get a name after creating a raid > device. So when assembling > a raid device, the name must not be null. So the dev and name can't be > null at the same time, right? Correct. NeilBrown > > Best Regards > Xiao > > > > Signed-off-by: NeilBrown <neilb@xxxxxxx> > > --- > > mdopen.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/mdopen.c b/mdopen.c > > index d18c931996d2..810f79a3d19a 100644 > > --- a/mdopen.c > > +++ b/mdopen.c > > @@ -370,6 +370,7 @@ int create_mddev(char *dev, char *name, int autof, int trustworthy, > > } > > if (block_udev) > > udev_block(devnm); > > + create_named_array(devnm); > > } > > > > sprintf(devname, "/dev/%s", devnm); > > -- > > 2.39.2 > > > >
