[dm-devel] [PATCH 01/12] libmultipath: add wwid for "struct uevent" to record wwid of uevent
Benjamin Marzinski
bmarzins at redhat.com
Thu Jan 5 17:36:47 UTC 2017
On Thu, Jan 05, 2017 at 11:10:43AM +0800, tang.junhui at zte.com.cn wrote:
> Hello Ben,
>
> I know what you concern about. Maybe we can change the "wwid" member
> in "struct uevent" to another name such as "merge_id" to only
> identify which uevents can merge together. The value of "merge_id" can
> set by "ID_SERIAL" or "ID_UID" in uevent. If we get the "merge_id"
> from uevents, we can merge and process it as merging way, otherwise
> we process it as old way (processed one by one).
> And we revert this patch:
> "[dm-devel] [PATCH 12/12] libmultipath: use existing wwid when wwid
> has already been existed in uevent"
> thus wwid of each path will get by methods of configuration as old
> ways.
>
> The premise is that, devices whose "merge_id" is the same have the
> same "wwid". I think this premise can be established.
So, if you have device where the merge_id doesn't equal the wwid, you
call domap on that device, as it it wasn't part of a merged set?
That would work, but you would have to be careful to deal with the case
where the last uevent in the set, the one that would be used to call
domap for the whole merged set, suddenly gets processed all on it's own,
because it had a different wwid from the rest of the set. In that case
You would need to make sure that something called domap on the other
members of the merged set. Now, I admit that this is a very unlikely
thing to happen.
I thought about proposing that we revert patch 12, but it does add
complexity if you find that only some of your merged devices change
wwid. Also, if all of them change to the same new wwid, you just skipped
merging when you should be able to. But I'm not against reverting it, as
long as we handle everything o.k. Reverting it would mean that we don't
have to worry about removing a capability that multipath previously had.
There's just a trade-off between supporting a capability (that we don't
know if anyone uses), and maintaining less complex code.
As long as it is possible to configure what uevent variable you check
for by device type, I don't know of a situation where this will cause
real world problems. It's possible that some users are changing
uid_attribute for only certain scsi-based arrays, but I don't know of
any cases. If somebody reading this knows of any cases, please speak up.
But I would like to have the variable you check be configurable so that
it's flexible with regards to new device types or the possiblity of
differing uevent variable names either between distributions or over
time. Does that sound reasonable?
-Ben
>
> how do you think about the above proposal?
>
> > The other option would be to not actually merge the uevents, but
> simply
> > run through the filtered but unmerged list of uevents, and skip the
> > domap stuff but remember the maps that need pushing to device-mapper.
> > Once you are done processing all the uevents, except for updating the
> > maps in device-mapper, you go back and update all the maps that need
> > updating. There's more code refactoring in this approach, but it
> keeps
> > the uid being set in pathinfo, where you have all the information
> > necessary to set it using uid_attribute, getuid, or specialized code
> > like rbd uses.
> I think it is ok, but a little complex. and if we can get rid of the
> "wwid" issue, we do not need to do so.
>
> Regards
> Tang Junhui
>
> 发件人: "Benjamin Marzinski" <bmarzins at redhat.com>
> 收件人: tang.junhui at zte.com.cn,
> 抄送: tang.wenjun3 at zte.com.cn, zhang.kai16 at zte.com.cn,
> dm-devel at redhat.com, bart.vanassche at sandisk.com, mwilck at suse.com
> 日期: 2017/01/05 02:23
> 主题: Re: [dm-devel] [PATCH 01/12] libmultipath: add wwid for
> "struct uevent" to record wwid of uevent
> 发件人: dm-devel-bounces at redhat.com
>
> --------------------------------------------------------------------------
>
> On Wed, Jan 04, 2017 at 02:56:46PM +0800, tang.junhui at zte.com.cn wrote:
> > Hello Ben,
> >
> > > Right now, multipath users are allowed configure devices to set the
> wwid
> > > based on any udev environment variable (or even use a callout,
> although
> > > this is deprecated). With this patch, that breaks.
> > Does WWID obtained by different methods change? If it changes, we
> would
> > better to modify code to keep it no change.
>
> Yes. users can pick any udev environment variable (and currently, any
> callout program that they write) to use as the wwid.
>
> > > If the udev sets
> > > ID_SERIAL for a device, that is its wwid, right?
> > Yes
> >
> > > Do you know if rbd
> > > devices have ID_SERIAL set?
> > WWID has different label in uevents for different devices, I only
> test for
> > SCSI devices.
>
> Where is that check? I only see a check for whether ID_SERIAL exists. If
> it exists on things that are not scsi devices, you will set the wwid for
> these devices with it as well, even if it doesn't work for them.
>
> > Now we do not support rbd divice for uevents merging, these
> > device process as old way, it has no harm in logic. If we need to
> merge
> > rbd uevents for these devices, we can add code to get wwid from
> uevents
> > and it can be supported easily.
>
> Look at get_rbd_uid(), and how it's called. rbd devices don't even use
> the getuid callout or uid_attribute. They use special code called by
> get_uid.
>
> Now you could add explicit checks so we only check ID_SERIAL for scsi
> devices, ID_UID for dasd devices, and never set the wwid otherwise. You
> could even make the attribute we check configurable by device type with
> an option like
>
> uid_attrs "sd:ID_SERIAL dasd:ID_UID"
>
> in the defaults section, that would set up mappings between device types
> and uevent attributes to check for the uid. But this would be on per
> device types, not per storage array, like it currently is. uid_attribute
> and getuid attribute would only ever be used for device types that
> weren't in the uid_attrs list.
>
> The other option would be to not actually merge the uevents, but simply
> run through the filtered but unmerged list of uevents, and skip the
> domap stuff but remember the maps that need pushing to device-mapper.
> Once you are done processing all the uevents, except for updating the
> maps in device-mapper, you go back and update all the maps that need
> updating. There's more code refactoring in this approach, but it keeps
> the uid being set in pathinfo, where you have all the information
> necessary to set it using uid_attribute, getuid, or specialized code
> like rbd uses.
>
> As long as we make sure that we are only checking specific uevent
> attributes for specific device types, I'm o.k. with your way, but we are
> losing flexibility that multipath has always had in regards to setting
> the wwid. I want to point that out so that anyone who needs this knows
> that it is changing.
>
> -Ben
>
> > Regards
> > Tang Junhui
> >
> > ������: "Benjamin Marzinski" <bmarzins at redhat.com>
> > �ռ���: tang.junhui at zte.com.cn,
> > ����: christophe.varoqui at opensvc.com, hare at suse.de,
> > mwilck at suse.com, bart.vanassche at sandisk.com, dm-devel at redhat.com,
> > zhang.kai16 at zte.com.cn, tang.wenjun3 at zte.com.cn
> > ����: 2017/01/04 06:03
> > ����: Re: [PATCH 01/12] libmultipath: add wwid for "struct
> uevent"
> > to record wwid of uevent
> >
> >
> --------------------------------------------------------------------------
> >
> > On Tue, Dec 27, 2016 at 04:03:18PM +0800, tang.junhui at zte.com.cn
> wrote:
> > > From: tang.junhui <tang.junhui at zte.com.cn>
> > >
> > > Add "char *wwid" to point WWID of uevent. This member identifies
> > > the LUN ID which the path belongs to, and it is used for merging
> > > uevents. WWID possibly did not exist in uevent yet, so ->wwid
> > > would be NULL, those uevents would not be merged, but be proccessed
> > > as old way.
> >
> > Right now, multipath users are allowed configure devices to set the
> wwid
> > based on any udev environment variable (or even use a callout,
> although
> > this is deprecated). With this patch, that breaks. If the udev sets
> > ID_SERIAL for a device, that is its wwid, right? Do you know if rbd
> > devices have ID_SERIAL set? If so, this change will break them. Even
> if
> > this change doesn't break any devices in their default
> configurations,
> > we would need to disallow changing how the wwid is set for this patch
> > to be safe.
> >
> > -Ben
> >
> > >
> > > Change-Id: Ie6b076363b3735dc7de10184b27fa799b499af0e
> > > Signed-off-by: tang.junhui <tang.junhui at zte.com.cn>
> > > ---
> > > libmultipath/uevent.c | 2 ++
> > > libmultipath/uevent.h | 1 +
> > > 2 files changed, 3 insertions(+)
> > >
> > > diff --git a/libmultipath/uevent.c b/libmultipath/uevent.c
> > > index 7edcce1..ef1bafe 100644
> > > --- a/libmultipath/uevent.c
> > > +++ b/libmultipath/uevent.c
> > > @@ -424,6 +424,8 @@ struct uevent *uevent_from_udev_device(struct
> > udev_device *dev)
> > > uev->devpath =
> > uev->envp[i] + 8;
> > > if (strcmp(name, "ACTION") == 0)
> > > uev->action =
> > uev->envp[i] + 7;
> > > + if (strcmp(name, "ID_SERIAL") ==
> 0)
> > > + uev->wwid =
> > uev->envp[i] + 10;
> > > i++;
> > > if (i == HOTPLUG_NUM_ENVP - 1)
> > > break;
> > > diff --git a/libmultipath/uevent.h b/libmultipath/uevent.h
> > > index 9d22dcd..7bfccef 100644
> > > --- a/libmultipath/uevent.h
> > > +++ b/libmultipath/uevent.h
> > > @@ -22,6 +22,7 @@ struct uevent {
> > > char *devpath;
> > > char *action;
> > > char *kernel;
> > > + char *wwid;
> > > unsigned long seqnum;
> > > char *envp[HOTPLUG_NUM_ENVP];
> > > };
> > > --
> > > 2.8.1.windows.1
> > >
>
> --
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