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storage: Fix algorithm generating path names for devmapper

Browse Source 
https://bugzilla.redhat.com/show_bug.cgi?id=1265694

Commit id '020135dc' didn't quite get the algorithm correct when a
device mapper source ended with a non numeric value (e.g. ends with
an alphabet value).

This patch modifies the 'part_separator' logic to add the "p" separator
to the attempted target path name only when specified as part_separator='yes'.

For a source name that already ends with a number, the logic doesn't change
as the part separator would need to be there.

For a source name that ends with something other than a number, this allows
the possibility that a "p" separator can be added. The default for one of
these source devices is to not add the separator.

The key for device mapper and the need for a partition separator "p" is
the presence of a number in the last character of the device name link
in /dev/mapper.  A name such as "/dev/mapper/mpatha1" would generate
a "/dev/mapper/mpatha1p1" partition, while "/dev/mapper/mpatha" would
generate partition "/dev/mapper/mpatha1". Similarly for a device
mapper entry not using friendly names or an alias, a device such as
"/dev/mapper/3600a0b80005b10ca00005ad656fd8d93" would generate a
paritition "/dev/mapper/3600a0b80005b10ca00005ad656fd8d93p1", while
a device such as "/dev/mapper/3600a0b80005b10ca00005e115729093f" would
generate a partition "/dev/mapper/3600a0b80005b10ca00005e115729093f1".
The long number is the WWID of the device. It's also possible to assign
an alias for a device mapper entry, that alias follows the same rules
with respect to ending with a number or not when adding a "p" to create
the target device path.
This commit is contained in:
John Ferlan 2016-05-09 14:57:17 -04:00
parent 5e54361c9d
commit e7bde8d319
3 changed files with 16 additions and 22 deletions
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18
docs/formatstorage.html.in
View File

@ -134,19 +134,11 @@
<code>path</code> may be supplied. Valid values for the attribute
may be either "yes" or "no". This attribute is to be used for a
<code>disk</code> pool type using a <code>path</code> to a
device mapper multipath device configured to utilize either
'user_friendly_names' or a custom 'alias' name in the
/etc/multipath.conf. The attribute directs libvirt to not
generate device volume names with the partition character "p".
By default, when libvirt generates the partition names for
device mapper multipath devices it will add a "p" path separator
to the device name before adding the partition number. For example,
a <code>device path</code> of '/dev/mapper/mpatha' libvirt would
generate partition names of '/dev/mapper/mpathap1',
'/dev/mapper/mpathap2', etc. for each partition found. With
this attribute set to "no", libvirt will not append the "p" to
the name unless it ends with a number thus generating names
of '/dev/mapper/mpatha1', '/dev/mapper/mpatha2', etc.
device mapper multipath device. Setting the attribute to "yes"
causes libvirt to attempt to generate and find target volume path's
using a "p" separator. The default algorithm used by device mapper
is to add the "p" separator only when the source device path ends
with a number.
<span class="since">Since 1.3.1</span></p></dd>
<dt><code>dir</code></dt>
<dd>Provides the source for pools backed by directories (pool

11
src/storage/parthelper.c
View File

@ -69,7 +69,7 @@ int main(int argc, char **argv)
const char *path;
char *canonical_path;
const char *partsep;
bool devmap_nopartsep = false;
bool devmap_partsep = false;
if (virGettextInitialize() < 0)
exit(EXIT_FAILURE);
@ -77,7 +77,7 @@ int main(int argc, char **argv)
if (argc == 3 && STREQ(argv[2], "-g")) {
cmd = DISK_GEOMETRY;
} else if (argc == 3 && STREQ(argv[2], "-p")) {
devmap_nopartsep = true;
devmap_partsep = true;
} else if (argc != 2) {
fprintf(stderr, _("syntax: %s DEVICE [-g]|[-p]\n"), argv[0]);
return 1;
@ -85,10 +85,11 @@ int main(int argc, char **argv)
path = argv[1];
if (virIsDevMapperDevice(path)) {
/* The 'devmap_nopartsep' option will not append the partsep of "p"
* onto the name unless the 'path' ends in a number
/* If the path ends with a number or we explicitly request it for
* path, then append the "p" partition separator. Otherwise, if
* the path ends with a letter already, then no need for a separator.
*/
if (c_isdigit(path[strlen(path)-1]) || !devmap_nopartsep)
if (c_isdigit(path[strlen(path)-1]) || devmap_partsep)
partsep = "p";
else
partsep = "";

9
src/storage/storage_backend_disk.c
View File

@ -325,13 +325,14 @@ virStorageBackendDiskReadPartitions(virStoragePoolObjPtr pool,
pool->def->source.devices[0].path,
NULL);
/* Check for the presence of the part_separator='no'. Pass this
/* Check for the presence of the part_separator='yes'. Pass this
* along to the libvirt_parthelper as option '-p'. This will cause
* libvirt_parthelper to not append the "p" partition separator to
* the generated device name, unless the name ends with a number.
* libvirt_parthelper to append the "p" partition separator to
* the generated device name for a source device which ends with
* a non-numeric value (e.g. mpatha would generate mpathap#).
*/
if (pool->def->source.devices[0].part_separator ==
VIR_TRISTATE_BOOL_NO)
VIR_TRISTATE_BOOL_YES)
virCommandAddArg(cmd, "-p");
/* If a volume is passed, virStorageBackendDiskMakeVol only updates the