Name
----
Timezone cache renewal in ctime(3C) (aka No reboot on timezone update)

Background
----------
Timezone patches contain the updates of the zoneinfo database files.

Internally libc caches the timezone information and never rereads
it. This means that when the timezone patches are applied and updates
are made to the zoneinfo database, files they are not activated until
the system is rebooted or the various process that use the timezone
information are restarted.

The impact of a reboot for the changes in the timezone is significant
especially for those customers with many Sun servers running many 
domains.

Customers have requested that when applying timezone patches, a
reboot is not required.  To satisfy the requirement, the timezone
code could check if the zoneinfo database files have been updated
since the last time by issuing the stat(2) system call. However, as
stat() is an expensive system call, the addition of the stat() call
would result in a great performance regression in the timezone code
in libc. Therefore, a more efficient method that notifies libc that
the zoneinfo database has been updated needs to be introduced.

Proposal
--------
All the ctime(3C) and mktime(3C) functions will use a semaphore on
per zone shared memory pages. The semaphore can be attached to process
by using mmap(2) to a software driver. The software driver allows
mmap() to attach the shared memory page for semaphore, and also allows
a privileged ioctl (requires PRIV_PROC_OWNER) to modify the memory
contents(semaphore) for the zone. The software driver also allows to
modify the memory contents for all zones (additionally requires
PRIV_PROC_ZONE). The reason for using a software driver is solely to
protect the shared memory from being released, invalidated or corrupted.

The ctime(3C) and mktime(3C) functions will test the semaphore before
using cache'd timezone information and, if it has changed, purge the
cache and re-read the zoneinfo file. No privilege is required to
test the semaphore. If the libc failed to open the device file,
ctime(3C) and mktime(3C) will not cache the timezone information.

When zoneinfo database files are updated, a new utility tzreload(1M)
can be executed, by a privileged user, to propagate the change (update
the semaphore status on the shared memory). All subsequent calls to
ctime(3C) functions from any processes within the system will reread
the updated zoneinfo database file. tzreload command will be added to
the "Process Management" RBAC profile.

Interfaces
----------
NAME			STABILITY		DESCRIPTION
-------------------------------------------------------------------
TZSYNCIOC_INC		Consolidation Private	ioctl to increment
						semaphore value.
TZSYNCIOC_INC_ALL_ZONES Consolidation Private	ioctl to increment
						semaphore value in all
						zones.
/dev/tzsync		Uncommitted		A device driver file to be
                                                used to mmap the semaphore
                                                memory.
/usr/sbin/tzreload	Committed		man page tzreload(1M)

Release
-------
A patch binding is requested.

Bug/RFEs
-------
6751272 RFE: Solaris timezone patches should not require reboot