[PATCH 0/1] RFC: Use /dev/md/X as default name

[PATCH 0/1] RFC: Use /dev/md/X as default name

[Jes.Sorensen]

From: Jes Sorensen <Jes.Sorensen@redhat.com>

I have received some issues for when creating an array using a
/dev/mdX name, the matching symlink in /dev/md/X isn't
created. Whereas if you create /dev/md/X, /dev/mdX is created
automatically.

I was trying to see if there was a better way of dealing with this,
but I couldn't find one. If you have suggestions for a better solution
I am all ears.

Thoughts?

Jes

Jes Sorensen (1):
  mddev_create(): choose /dev/md/ name over /dev/mdX

 mdopen.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

-- 
2.1.0

[PATCH 1/1] mddev_create(): choose /dev/md/ name over /dev/mdX

[Jes.Sorensen]

From: Jes Sorensen <Jes.Sorensen@redhat.com>

/dev/mdX is created automatically if we create /dev/md/X, but
/dev/md/X isn't created automatically if we create /dev/mdX.

By chosing /dev/md/X as the default name from /dev/mdX, we achieve
consistency when creating new arrays.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
---
 mdopen.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mdopen.c b/mdopen.c
index 2c9d745..db75d09 100644
--- a/mdopen.c
+++ b/mdopen.c
@@ -338,7 +338,11 @@ int create_mddev(char *dev, char *name, int autof, int trustworthy,
 
 	sprintf(devname, "/dev/%s", devnm);
 
-	if (dev && dev[0] == '/')
+	if (dev && strncmp(dev, "/dev/md", 7) == 0 &&
+	    dev[7] != '/' && strlen(dev) > 7) {
+		strcpy(chosen, "/dev/md/");
+		strcpy(chosen + 8, dev + 7);
+	} else if (dev && dev[0] == '/')
 		strcpy(chosen, dev);
 	else if (cname[0] == 0)
 		strcpy(chosen, devname);
-- 
2.1.0

Re: [PATCH 0/1] RFC: Use /dev/md/X as default name

[Jes Sorensen]

Jes.Sorensen@redhat.com writes:
> From: Jes Sorensen <Jes.Sorensen@redhat.com>
>
> I have received some issues for when creating an array using a
> /dev/mdX name, the matching symlink in /dev/md/X isn't
> created. Whereas if you create /dev/md/X, /dev/mdX is created
> automatically.
>
> I was trying to see if there was a better way of dealing with this,
> but I couldn't find one. If you have suggestions for a better solution
> I am all ears.
>
> Thoughts?

Hi Neil,

Any thoughts on this one?

Cheers,
Jes

>
> Jes
>
> Jes Sorensen (1):
>   mddev_create(): choose /dev/md/ name over /dev/mdX
>
>  mdopen.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)

Re: [PATCH 0/1] RFC: Use /dev/md/X as default name

[NeilBrown]

[-- Attachment #1: Type: text/plain, Size: 1512 bytes --]

On Wed, 18 Feb 2015 13:12:09 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
wrote:

> Jes.Sorensen@redhat.com writes:
> > From: Jes Sorensen <Jes.Sorensen@redhat.com>
> >
> > I have received some issues for when creating an array using a
> > /dev/mdX name, the matching symlink in /dev/md/X isn't
> > created. Whereas if you create /dev/md/X, /dev/mdX is created
> > automatically.
> >
> > I was trying to see if there was a better way of dealing with this,
> > but I couldn't find one. If you have suggestions for a better solution
> > I am all ears.
> >
> > Thoughts?
> 
> Hi Neil,
> 
> Any thoughts on this one?

Thanks for the reminder....

I'm not sure that I really see the problem.

  "I ask it to create /dev/mdX and it doesn't create /dev/md/X".

Well ... no.  You didn't ask it to.  If you want it to create /dev/md/X,
then ... ask it to.

/dev/mdX is the canonical name.  It always gets created.
/dev/md/X is a convenient alias.  It gets created if requested.

Is there really a problem here worth solving?

Maybe I missed something.

NeilBrown

> 
> Cheers,
> Jes
> 
> >
> > Jes
> >
> > Jes Sorensen (1):
> >   mddev_create(): choose /dev/md/ name over /dev/mdX
> >
> >  mdopen.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 811 bytes --]

Re: [PATCH 0/1] RFC: Use /dev/md/X as default name

[Jes Sorensen]

NeilBrown <neilb@suse.de> writes:
> On Wed, 18 Feb 2015 13:12:09 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
> wrote:
>
>> Jes.Sorensen@redhat.com writes:
>> > From: Jes Sorensen <Jes.Sorensen@redhat.com>
>> >
>> > I have received some issues for when creating an array using a
>> > /dev/mdX name, the matching symlink in /dev/md/X isn't
>> > created. Whereas if you create /dev/md/X, /dev/mdX is created
>> > automatically.
>> >
>> > I was trying to see if there was a better way of dealing with this,
>> > but I couldn't find one. If you have suggestions for a better solution
>> > I am all ears.
>> >
>> > Thoughts?
>> 
>> Hi Neil,
>> 
>> Any thoughts on this one?
>
> Thanks for the reminder....
>
> I'm not sure that I really see the problem.
>
>   "I ask it to create /dev/mdX and it doesn't create /dev/md/X".
>
> Well ... no.  You didn't ask it to.  If you want it to create /dev/md/X,
> then ... ask it to.
>
> /dev/mdX is the canonical name.  It always gets created.
> /dev/md/X is a convenient alias.  It gets created if requested.
>
> Is there really a problem here worth solving?
>
> Maybe I missed something.

I have had complaints in Fedora from the installer people that they rely
on the /dev/md/ name being created when they create a new device. It is
also inconsistent because /dev/md/<X> will be created if you run
'mdadm -As' later on.

I don't see it as a major issue, but I can see why it is frustrating for
some and I think there is something to be said for being consistent in
behavior.

Cheers,
Jes

Re: [PATCH 0/1] RFC: Use /dev/md/X as default name

[NeilBrown]

[-- Attachment #1: Type: text/plain, Size: 2738 bytes --]

On Wed, 18 Feb 2015 17:11:33 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
wrote:

> NeilBrown <neilb@suse.de> writes:
> > On Wed, 18 Feb 2015 13:12:09 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
> > wrote:
> >
> >> Jes.Sorensen@redhat.com writes:
> >> > From: Jes Sorensen <Jes.Sorensen@redhat.com>
> >> >
> >> > I have received some issues for when creating an array using a
> >> > /dev/mdX name, the matching symlink in /dev/md/X isn't
> >> > created. Whereas if you create /dev/md/X, /dev/mdX is created
> >> > automatically.
> >> >
> >> > I was trying to see if there was a better way of dealing with this,
> >> > but I couldn't find one. If you have suggestions for a better solution
> >> > I am all ears.
> >> >
> >> > Thoughts?
> >> 
> >> Hi Neil,
> >> 
> >> Any thoughts on this one?
> >
> > Thanks for the reminder....
> >
> > I'm not sure that I really see the problem.
> >
> >   "I ask it to create /dev/mdX and it doesn't create /dev/md/X".
> >
> > Well ... no.  You didn't ask it to.  If you want it to create /dev/md/X,
> > then ... ask it to.
> >
> > /dev/mdX is the canonical name.  It always gets created.
> > /dev/md/X is a convenient alias.  It gets created if requested.
> >
> > Is there really a problem here worth solving?
> >
> > Maybe I missed something.
> 
> I have had complaints in Fedora from the installer people that they rely
> on the /dev/md/ name being created when they create a new device. It is
> also inconsistent because /dev/md/<X> will be created if you run
> 'mdadm -As' later on.

If they rely on the /dev/md/ name being created, then surely they should ask
for it to be created.
Is it really harder to run "mdadm -C /dev/md/0" than "mdadm -C /dev/md0" ??

If you create an array as "/dev/md0", then after subsequent "mdadm
-As" /dev/md0 will exist.
If you create an array as "/dev/md/0", then after subsequent mdadm
-As", /dev/md/0 will exist.

The fact that something unasked for also exists is a bonus.

> 
> I don't see it as a major issue, but I can see why it is frustrating for
> some and I think there is something to be said for being consistent in
> behavior.

I think the behaviour is perfectly consistent.  It just follows rules that
are slightly less trivial that some people appear to want.

However....
If you changed

			mp = map_by_uuid(&map, info->uuid);
			if (mp && mp->path &&
			    strncmp(mp->path, "/dev/md/", 8) == 0) {
				printf("MD_DEVNAME=");
				print_escape(mp->path+8);
				putchar('\n');
			}


in Detail.c so that when mp->path were "/dev/md0", MD_DEVNAME became "0",
then you should get the result that you are after, and I probably wouldn't
object to the patch.

NeilBrown 


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 811 bytes --]

Re: [PATCH 0/1] RFC: Use /dev/md/X as default name

[Jes Sorensen]

NeilBrown <neilb@suse.de> writes:
> On Wed, 18 Feb 2015 17:11:33 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
> wrote:
>
>> NeilBrown <neilb@suse.de> writes:
>> > On Wed, 18 Feb 2015 13:12:09 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
>> > wrote:
>> >
>> >> Jes.Sorensen@redhat.com writes:
>> >> > From: Jes Sorensen <Jes.Sorensen@redhat.com>
>> >> >
>> >> > I have received some issues for when creating an array using a
>> >> > /dev/mdX name, the matching symlink in /dev/md/X isn't
>> >> > created. Whereas if you create /dev/md/X, /dev/mdX is created
>> >> > automatically.
>> >> >
>> >> > I was trying to see if there was a better way of dealing with this,
>> >> > but I couldn't find one. If you have suggestions for a better solution
>> >> > I am all ears.
>> >> >
>> >> > Thoughts?
>> >> 
>> >> Hi Neil,
>> >> 
>> >> Any thoughts on this one?
>> >
>> > Thanks for the reminder....
>> >
>> > I'm not sure that I really see the problem.
>> >
>> >   "I ask it to create /dev/mdX and it doesn't create /dev/md/X".
>> >
>> > Well ... no.  You didn't ask it to.  If you want it to create /dev/md/X,
>> > then ... ask it to.
>> >
>> > /dev/mdX is the canonical name.  It always gets created.
>> > /dev/md/X is a convenient alias.  It gets created if requested.
>> >
>> > Is there really a problem here worth solving?
>> >
>> > Maybe I missed something.
>> 
>> I have had complaints in Fedora from the installer people that they rely
>> on the /dev/md/ name being created when they create a new device. It is
>> also inconsistent because /dev/md/<X> will be created if you run
>> 'mdadm -As' later on.
>
> If they rely on the /dev/md/ name being created, then surely they should ask
> for it to be created.
> Is it really harder to run "mdadm -C /dev/md/0" than "mdadm -C /dev/md0" ??
>
> If you create an array as "/dev/md0", then after subsequent "mdadm
> -As" /dev/md0 will exist.
> If you create an array as "/dev/md/0", then after subsequent mdadm
> -As", /dev/md/0 will exist.
>
> The fact that something unasked for also exists is a bonus.
>
>> 
>> I don't see it as a major issue, but I can see why it is frustrating for
>> some and I think there is something to be said for being consistent in
>> behavior.
>
> I think the behaviour is perfectly consistent.  It just follows rules that
> are slightly less trivial that some people appear to want.
>
> However....
> If you changed
>
> 			mp = map_by_uuid(&map, info->uuid);
> 			if (mp && mp->path &&
> 			    strncmp(mp->path, "/dev/md/", 8) == 0) {
> 				printf("MD_DEVNAME=");
> 				print_escape(mp->path+8);
> 				putchar('\n');
> 			}
>
>
> in Detail.c so that when mp->path were "/dev/md0", MD_DEVNAME became "0",
> then you should get the result that you are after, and I probably wouldn't
> object to the patch.

Neil,

Finally had time to go back and look at this - I don't quite understand
your request here.

As far as I can see, the above code isn't run at all during device
creation, so I don't get how modifying it as you suggest will make
/dev/md/111 appear if I create /dev/md111?

Cheers,
Jes

Re: [PATCH 0/1] RFC: Use /dev/md/X as default name

[NeilBrown]

[-- Attachment #1: Type: text/plain, Size: 3993 bytes --]

On Mon, 02 Mar 2015 11:32:16 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
wrote:

> NeilBrown <neilb@suse.de> writes:
> > On Wed, 18 Feb 2015 17:11:33 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
> > wrote:
> >
> >> NeilBrown <neilb@suse.de> writes:
> >> > On Wed, 18 Feb 2015 13:12:09 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
> >> > wrote:
> >> >
> >> >> Jes.Sorensen@redhat.com writes:
> >> >> > From: Jes Sorensen <Jes.Sorensen@redhat.com>
> >> >> >
> >> >> > I have received some issues for when creating an array using a
> >> >> > /dev/mdX name, the matching symlink in /dev/md/X isn't
> >> >> > created. Whereas if you create /dev/md/X, /dev/mdX is created
> >> >> > automatically.
> >> >> >
> >> >> > I was trying to see if there was a better way of dealing with this,
> >> >> > but I couldn't find one. If you have suggestions for a better solution
> >> >> > I am all ears.
> >> >> >
> >> >> > Thoughts?
> >> >> 
> >> >> Hi Neil,
> >> >> 
> >> >> Any thoughts on this one?
> >> >
> >> > Thanks for the reminder....
> >> >
> >> > I'm not sure that I really see the problem.
> >> >
> >> >   "I ask it to create /dev/mdX and it doesn't create /dev/md/X".
> >> >
> >> > Well ... no.  You didn't ask it to.  If you want it to create /dev/md/X,
> >> > then ... ask it to.
> >> >
> >> > /dev/mdX is the canonical name.  It always gets created.
> >> > /dev/md/X is a convenient alias.  It gets created if requested.
> >> >
> >> > Is there really a problem here worth solving?
> >> >
> >> > Maybe I missed something.
> >> 
> >> I have had complaints in Fedora from the installer people that they rely
> >> on the /dev/md/ name being created when they create a new device. It is
> >> also inconsistent because /dev/md/<X> will be created if you run
> >> 'mdadm -As' later on.
> >
> > If they rely on the /dev/md/ name being created, then surely they should ask
> > for it to be created.
> > Is it really harder to run "mdadm -C /dev/md/0" than "mdadm -C /dev/md0" ??
> >
> > If you create an array as "/dev/md0", then after subsequent "mdadm
> > -As" /dev/md0 will exist.
> > If you create an array as "/dev/md/0", then after subsequent mdadm
> > -As", /dev/md/0 will exist.
> >
> > The fact that something unasked for also exists is a bonus.
> >
> >> 
> >> I don't see it as a major issue, but I can see why it is frustrating for
> >> some and I think there is something to be said for being consistent in
> >> behavior.
> >
> > I think the behaviour is perfectly consistent.  It just follows rules that
> > are slightly less trivial that some people appear to want.
> >
> > However....
> > If you changed
> >
> > 			mp = map_by_uuid(&map, info->uuid);
> > 			if (mp && mp->path &&
> > 			    strncmp(mp->path, "/dev/md/", 8) == 0) {
> > 				printf("MD_DEVNAME=");
> > 				print_escape(mp->path+8);
> > 				putchar('\n');
> > 			}
> >
> >
> > in Detail.c so that when mp->path were "/dev/md0", MD_DEVNAME became "0",
> > then you should get the result that you are after, and I probably wouldn't
> > object to the patch.
> 
> Neil,
> 
> Finally had time to go back and look at this - I don't quite understand
> your request here.
> 
> As far as I can see, the above code isn't run at all during device
> creation, so I don't get how modifying it as you suggest will make
> /dev/md/111 appear if I create /dev/md111?
> 
> Cheers,
> Jes

Wheels within wheels of deception and indirection....

mdadm doesn't create the devices directly, udev does that.

IMPORT{program}="BINDIR/mdadm --detail --export $devnode"
ENV{DEVTYPE}=="disk", ENV{MD_DEVNAME}=="?*", SYMLINK+="md/$env{MD_DEVNAME}"


So the symlink from /dev/md gets created iff "mdadm --detail --export"
reports an MD_DEVNAME.

Hence the change suggested.

mdadm *can* create the devices itself, but only if udev isn't running, or
mdamd has been explicitly told to ignore udev.  Normally that doesn't happen.

NeilBrown


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 811 bytes --]

Re: [PATCH 0/1] RFC: Use /dev/md/X as default name

[Jes Sorensen]

NeilBrown <neilb@suse.de> writes:
> On Mon, 02 Mar 2015 11:32:16 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
>> Neil,
>> 
>> Finally had time to go back and look at this - I don't quite understand
>> your request here.
>> 
>> As far as I can see, the above code isn't run at all during device
>> creation, so I don't get how modifying it as you suggest will make
>> /dev/md/111 appear if I create /dev/md111?
>> 
>> Cheers,
>> Jes
>
> Wheels within wheels of deception and indirection....
>
> mdadm doesn't create the devices directly, udev does that.
>
> IMPORT{program}="BINDIR/mdadm --detail --export $devnode"
> ENV{DEVTYPE}=="disk", ENV{MD_DEVNAME}=="?*", SYMLINK+="md/$env{MD_DEVNAME}"
>
>
> So the symlink from /dev/md gets created iff "mdadm --detail --export"
> reports an MD_DEVNAME.
>
> Hence the change suggested.
>
> mdadm *can* create the devices itself, but only if udev isn't running, or
> mdamd has been explicitly told to ignore udev.  Normally that doesn't happen.

Ahhh, I didn't see anything happening on my system, but it may be the
RHEL/Fedora udev rules file is missing something. I'll have to take a
closer look there!

Thanks!
Jes

Re: [PATCH 0/1] RFC: Use /dev/md/X as default name

[Jes Sorensen]

Jes Sorensen <Jes.Sorensen@redhat.com> writes:
> NeilBrown <neilb@suse.de> writes:
>> On Mon, 02 Mar 2015 11:32:16 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
>>> Neil,
>>> 
>>> Finally had time to go back and look at this - I don't quite understand
>>> your request here.
>>> 
>>> As far as I can see, the above code isn't run at all during device
>>> creation, so I don't get how modifying it as you suggest will make
>>> /dev/md/111 appear if I create /dev/md111?
>>> 
>>> Cheers,
>>> Jes
>>
>> Wheels within wheels of deception and indirection....
>>
>> mdadm doesn't create the devices directly, udev does that.
>>
>> IMPORT{program}="BINDIR/mdadm --detail --export $devnode"
>> ENV{DEVTYPE}=="disk", ENV{MD_DEVNAME}=="?*", SYMLINK+="md/$env{MD_DEVNAME}"
>>
>>
>> So the symlink from /dev/md gets created iff "mdadm --detail --export"
>> reports an MD_DEVNAME.
>>
>> Hence the change suggested.
>>
>> mdadm *can* create the devices itself, but only if udev isn't running, or
>> mdamd has been explicitly told to ignore udev.  Normally that doesn't happen.
>
> Ahhh, I didn't see anything happening on my system, but it may be the
> RHEL/Fedora udev rules file is missing something. I'll have to take a
> closer look there!

Actually I remember why I didn't get that far - I added some debug code
to the place you suggested I modify, and it never triggered during
Create.

Cheers,
Jes