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devices: improve handling of duplicate PVs

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Example:

/dev/loop0 and /dev/loop1 are duplicates,
created by copying one backing file to the
other.

'identity /dev/loopX' creates an identity
mapping for loopX named idmloopX, which
adds a duplicate for the named device.

The duplicate selection code for lvmetad is
incomplete, and lvmetad is disabled for this
example.

[~]# losetup -f loopfile0
[~]# pvs
  PV         VG           Fmt  Attr PSize   PFree
  /dev/loop0 foo          lvm2 a--  308.00m 296.00m

[~]# losetup -f loopfile1
[~]# pvs
  Found duplicate PV LnSOEqzEYED3RvIOa5PZP2s7uyuBLmAV: using /dev/loop1 not /dev/loop0
  Using duplicate PV /dev/loop1 which is more recent, replacing /dev/loop0
  PV         VG           Fmt  Attr PSize   PFree
  /dev/loop1 foo          lvm2 a--  308.00m 308.00m

[~]# ./identity /dev/loop0
[~]# pvs
  Found duplicate PV LnSOEqzEYED3RvIOa5PZP2s7uyuBLmAV: using /dev/loop1 not /dev/loop0
  Using duplicate PV /dev/loop1 without holders, replacing /dev/loop0
  Found duplicate PV LnSOEqzEYED3RvIOa5PZP2s7uyuBLmAV: using /dev/mapper/idmloop0 not /dev/loop1
  Using duplicate PV /dev/mapper/idmloop0 from subsystem DM, replacing /dev/loop1
  PV                   VG           Fmt  Attr PSize   PFree
  /dev/mapper/idmloop0 foo          lvm2 a--  308.00m 296.00m

[~]# ./identity /dev/loop1
[~]# pvs
  WARNING: duplicate PV LnSOEqzEYED3RvIOa5PZP2s7uyuBLmAV is being used from both devices /dev/loop0 and /dev/loop1
  Found duplicate PV LnSOEqzEYED3RvIOa5PZP2s7uyuBLmAV: using /dev/loop1 not /dev/loop0
  Using duplicate PV /dev/loop1 which is more recent, replacing /dev/loop0
  Found duplicate PV LnSOEqzEYED3RvIOa5PZP2s7uyuBLmAV: using /dev/mapper/idmloop0 not /dev/loop1
  Using duplicate PV /dev/mapper/idmloop0 from subsystem DM, replacing /dev/loop1
  Found duplicate PV LnSOEqzEYED3RvIOa5PZP2s7uyuBLmAV: using /dev/mapper/idmloop1 not /dev/mapper/idmloop0
  Using duplicate PV /dev/mapper/idmloop1 which is more recent, replacing /dev/mapper/idmloop0
  PV                   VG           Fmt  Attr PSize   PFree
  /dev/mapper/idmloop1 foo          lvm2 a--  308.00m 308.00m
This commit is contained in:
David Teigland 2015-04-24 14:58:58 -05:00
parent 6cc37275ce
commit beb229e1e8
3 changed files with 222 additions and 50 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

252
lib/cache/lvmcache.c vendored
View File

@ -1529,6 +1529,64 @@ void lvmcache_replace_dev(struct cmd_context *cmd, struct physical_volume *pv,
pv->dev = dev;
}
/*
* We can see multiple different devices with the
* same pvid, i.e. duplicates.
*
* There may be different reasons for seeing two
* devices with the same pvid:
* - multipath showing two paths to the same thing
* - one device copied to another, e.g. with dd,
* also referred to as cloned devices.
* - a "subsystem" taking a device and creating
* another device of its own that represents the
* underlying device it is using, e.g. using dm
* to create an identity mapping of a PV.
*
* Given duplicate devices, we have to choose one
* of them to be the "preferred" dev, i.e. the one
* that will be referenced in lvmcache, by pv->dev.
* We can keep the existing dev, that's currently
* used in lvmcache, or we can replace the existing
* dev with the new duplicate.
*
* Regardless of which device is preferred, we need
* to print messages explaining which devices were
* found so that a user can sort out for themselves
* what has happened if the preferred device is not
* the one they are interested in.
*
* If a user wants to use the non-preferred device,
* they will need to filter out the device that
* lvm is preferring.
*
* The dev_subsystem calls check if the major number
* of the dev is part of a subsystem like DM/MD/DRBD.
* A dev that's part of a subsystem is preferred over a
* duplicate of that dev that is not part of a
* subsystem.
*
* The has_holders calls check if the device is being
* used by another, and prefers one that's being used.
*
* FIXME: why do we prefer a device without holders
* over a device with holders? We should understand
* the reason for that choice.
*
* FIXME: there may be other reasons to prefer one
* device over another:
*
* . are there other use/open counts we could check
* beyond the holders?
*
* . check if either is bad/usable and prefer
* the good one?
*
* . prefer the one with smaller minor number?
* Might avoid disturbing things due to a new
* transient duplicate?
*/
struct lvmcache_info *lvmcache_add(struct labeller *labeller, const char *pvid,
struct device *dev,
const char *vgname, const char *vgid,
@ -1576,54 +1634,156 @@ struct lvmcache_info *lvmcache_add(struct labeller *labeller, const char *pvid,
lvmcache_del_bas(info);
} else {
if (existing->dev != dev) {
/* Is the existing entry a duplicate pvid e.g. md ? */
if (dev_subsystem_part_major(dt, existing->dev) &&
!dev_subsystem_part_major(dt, dev)) {
log_very_verbose("Ignoring duplicate PV %s on "
"%s - using %s %s",
pvid, dev_name(dev),
dev_subsystem_name(dt, existing->dev),
dev_name(existing->dev));
return NULL;
} else if (dm_is_dm_major(MAJOR(existing->dev->dev)) &&
!dm_is_dm_major(MAJOR(dev->dev))) {
log_very_verbose("Ignoring duplicate PV %s on "
"%s - using dm %s",
pvid, dev_name(dev),
dev_name(existing->dev));
return NULL;
} else if (!dev_subsystem_part_major(dt, existing->dev) &&
dev_subsystem_part_major(dt, dev))
log_very_verbose("Duplicate PV %s on %s - "
"using %s %s", pvid,
dev_name(existing->dev),
dev_subsystem_name(dt, existing->dev),
dev_name(dev));
else if (!dm_is_dm_major(MAJOR(existing->dev->dev)) &&
dm_is_dm_major(MAJOR(dev->dev)))
log_very_verbose("Duplicate PV %s on %s - "
"using dm %s", pvid,
dev_name(existing->dev),
dev_name(dev));
/* FIXME If both dm, check dependencies */
//else if (dm_is_dm_major(MAJOR(existing->dev->dev)) &&
//dm_is_dm_major(MAJOR(dev->dev)))
//
else if (!strcmp(pvid_s, existing->dev->pvid)) {
log_error("Found duplicate PV %s: using %s not %s",
pvid_s,
dev_name(existing->dev),
dev_name(dev));
strncpy(dev->pvid, pvid_s, sizeof(dev->pvid));
_found_duplicate_pvs = 1;
return NULL;
int old_in_subsystem = 0;
int new_in_subsystem = 0;
int old_is_dm = 0;
int new_is_dm = 0;
int old_has_holders = 0;
int new_has_holders = 0;
/*
* Here are different devices with the same pvid:
* duplicates. See comment above.
*/
/*
* This flag tells the process_each_pv code to search
* the devices list for duplicates, so that devices
* can be processed together with their duplicates
* (while processing the VG, rather than reporting
* pv->dev under the VG, and its duplicate outside
* the VG context.)
*/
_found_duplicate_pvs = 1;
/*
* The new dev may not have pvid set.
* The process_each_pv code needs to have the pvid
* set in each device to detect that the devices
* are duplicates.
*/
strncpy(dev->pvid, pvid_s, sizeof(dev->pvid));
/*
* Now decide if we are going to ignore the new
* device, or replace the existing/old device in
* lvmcache with the new one.
*/
old_in_subsystem = dev_subsystem_part_major(dt, existing->dev);
new_in_subsystem = dev_subsystem_part_major(dt, dev);
old_is_dm = dm_is_dm_major(MAJOR(existing->dev->dev));
new_is_dm = dm_is_dm_major(MAJOR(dev->dev));
old_has_holders = dm_device_has_holders(MAJOR(existing->dev->dev), MINOR(existing->dev->dev));
new_has_holders = dm_device_has_holders(MAJOR(dev->dev), MINOR(dev->dev));
if (old_has_holders && new_has_holders) {
/*
* This is not a selection of old or new, but
* just a warning to be aware of.
*/
log_warn("WARNING: duplicate PV %s is being used from both devices %s and %s",
pvid_s,
dev_name(existing->dev),
dev_name(dev));
}
if (old_in_subsystem && !new_in_subsystem) {
/* Use old, ignore new. */
log_warn("Found duplicate PV %s: using %s not %s",
pvid_s,
dev_name(existing->dev),
dev_name(dev));
log_warn("Using duplicate PV %s from subsystem %s, ignoring %s",
dev_name(existing->dev),
dev_subsystem_name(dt, existing->dev),
dev_name(dev));
return NULL;
} else if (!old_in_subsystem && new_in_subsystem) {
/* Use new, replace old. */
log_warn("Found duplicate PV %s: using %s not %s",
pvid_s,
dev_name(dev),
dev_name(existing->dev));
log_warn("Using duplicate PV %s from subsystem %s, replacing %s",
dev_name(dev),
dev_subsystem_name(dt, dev),
dev_name(existing->dev));
} else if (old_has_holders && !new_has_holders) {
/* Use new, replace old. */
/* FIXME: why choose the one without olders? */
log_warn("Found duplicate PV %s: using %s not %s",
pvid_s,
dev_name(dev),
dev_name(existing->dev));
log_warn("Using duplicate PV %s without holders, replacing %s",
dev_name(dev),
dev_name(existing->dev));
} else if (!old_has_holders && new_has_holders) {
/* Use old, ignore new. */
log_warn("Found duplicate PV %s: using %s not %s",
pvid_s,
dev_name(existing->dev),
dev_name(dev));
log_warn("Using duplicate PV %s without holders, ignoring %s",
dev_name(existing->dev),
dev_name(dev));
return NULL;
} else if (old_is_dm && new_is_dm) {
/* Use new, replace old. */
/* FIXME: why choose the new instead of the old? */
log_warn("Found duplicate PV %s: using %s not %s",
pvid_s,
dev_name(dev),
dev_name(existing->dev));
log_warn("Using duplicate PV %s which is more recent, replacing %s",
dev_name(dev),
dev_name(existing->dev));
} else if (!strcmp(pvid_s, existing->dev->pvid)) {
/* No criteria to use for preferring old or new. */
/* FIXME: why choose the new instead of the old? */
/* FIXME: a transient duplicate would be a reason
* to select the old instead of the new. */
log_warn("Found duplicate PV %s: using %s not %s",
pvid_s,
dev_name(dev),
dev_name(existing->dev));
log_warn("Using duplicate PV %s which is more recent, replacing %s",
dev_name(dev),
dev_name(existing->dev));
}
} else {
/*
* The new dev is the same as the existing dev.
*
* FIXME: Why can't we just return NULL here if the
* device already exists? Things don't seem to work
* if we do that for some reason.
*/
log_verbose("Found same device %s with same pvid %s",
dev_name(existing->dev), pvid_s);
}
if (strcmp(pvid_s, existing->dev->pvid))
log_debug_cache("Updating pvid cache to %s (%s) from %s (%s)",
pvid_s, dev_name(dev),
existing->dev->pvid, dev_name(existing->dev));
/* Switch over to new preferred device */
/*
* FIXME: when could this ever happen?
* If this does happen, identify when/why here, and
* if not, remove this code.
*/
if (strcmp(pvid_s, existing->dev->pvid)) {
log_warn("Replacing dev %s pvid %s with dev %s pvid %s",
dev_name(existing->dev), existing->dev->pvid,
dev_name(dev), pvid_s);
}
/*
* Switch over to new preferred device.
*/
existing->dev = dev;
info = existing;
/* Has labeller changed? */

17
lib/cache/lvmetad.c vendored
View File

@ -366,10 +366,19 @@ static struct lvmcache_info *_pv_populate_lvmcache(struct cmd_context *cmd,
while (alt_device) {
dev_alternate = dev_cache_get_by_devt(alt_device->v.i, cmd->filter);
if (dev_alternate)
lvmcache_add(fmt->labeller, (const char *)&pvid, dev_alternate,
vgname, (const char *)&vgid, 0);
else
if (dev_alternate) {
if ((info = lvmcache_add(fmt->labeller, (const char *)&pvid, dev_alternate,
vgname, (const char *)&vgid, 0))) {
/*
* FIXME: when lvmcache_add returns non-NULL,
* it means that it has made dev_alternate
* the preferred device in lvmcache.
* I think that means it should be followed
* by the same steps done above?
*/
log_warn("lvmcache only partially updated for alternate device %s", dev_name(dev));
}
} else
log_warn("Duplicate of PV %s dev %s exists on unknown device %"PRId64 ":%" PRId64,
pvid_txt, dev_name(dev), MAJOR(alt_device->v.i), MINOR(alt_device->v.i));
alt_device = alt_device->next;

3
lib/device/dev-type.c
View File

@ -225,6 +225,9 @@ int dev_subsystem_part_major(struct dev_types *dt, struct device *dev)
const char *dev_subsystem_name(struct dev_types *dt, struct device *dev)
{
if (MAJOR(dev->dev) == dt->device_mapper_major)
return "DM";
if (MAJOR(dev->dev) == dt->md_major)
return "MD";