Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

In snmp_hostres, device_map table is used for consistent device table
indexing. When a device has gone it is not removed from device_map
table but just its entry_p field is set to NULL.

So when traversing device_map in disk_OS_get_ATA_disks() and
disk_OS_get_MD_disks() check for entry_p being NULL, otherwise the
bsnmpd crash is possible when a removed map entry is dereferenced.

Before the fix, for disk_OS_get_ATA_disks() the crash could be easily
reproduced running:

atacontrol detach ata1

The crash was not observed in disk_OS_get_MD_disks() because currently
snmp_hostres does no see md(4) disks: to get the device list it uses
devinfo(3), which does not return md devices.

Reported by: Miroslav Lachman 000.fbsd quip.cz
MFC after: 1 week

Apparently, "ada" drives are better treated similarly to "da" drives.

It seems that the warning is much less severe than its message says. The
device is certainly added to the list after the first pass.

Fix typo

MFC after: 1 month

Make failed open of /dev/mdctl in the bsnmpd hostres module non-fatal.
This makes it possible to use the hostres module when bsnmpd is not
running as root.

MFC after: 1 week

Reduce the memory requirements for the tables by (1) using malloced strings
instead of maximum sized arrays embedded in the table structures and (2)
using pointers to constant oids instead of copying the oid into each
table structure. This also fixes indexing in the case when a string used
for indexing is longer than the maximum size allowed in the MIB.

Submitted by: Victor Cruceru <soc-victor@>

Fix false positives when searching for disks. Things like adv(4) are not
disks.

Submitted by: Victor Cruceru <soc-victor@>

Fix the MIB to use libgeom instead of libdisk.

Submitted by: Victor Cruceru <soc-victor>

Forced commit because I lost the commit message in the previous commit:

This is the implementation of the HOSTRES MIB that was developed by
Victor during SoC 2005 with some stylification by philip@ and harti@.

Submitted by: Victor Cruceru <soc-victor@freebsd.org>
Reviewed by: philip, harti

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