PCFS mount options "noatime"/"atime" [PSARC/2007/415 FastTrack timeout 07/24/2007]

[Peter Dennis - Solaris Sustaining Engineering]

[resending this as it would appear the initial submission of it has not
  reached some folks]

I am sponsoring this fasttrack for Frank Hofmann.

The Release Binding is patch and the Interface is Committed for the new
flags.

Thanks
pete


Case:           PCFS mount options "noatime"/"atime"

Author:         Frank Hofmann

Summary:
         This proposal requests
         * to introduce a mount option pair for PCFS, "-o noatime" resp.
           "-o atime", which suppresses / enables creating access time
           updates.
         * to disable access time updates (use the "-o noatime" option by
           default) for PCFS if it is used on removeable media.

         The Release Binding is patch and the Interface is Committed.

The Problem
         Flash-based removeable media can only perform a limited amount
         of write cycles. In addition to that, writes on such media are
         very slow (compared to reads). Since PCFS is frequently used
         on such devices ("memory sticks"), attempts should be made to
         minimize media write access whenever possible. Access timestamps
         are an easy target for that objective, because:
                 - FAT access timestamps are day-granular
                 - FAT access timestamps are optional as per FAT spec

         In addition, UFS has had the "noatime" mount option since 1998.
         PCFS should have it as well.

The Proposed Solution
         PCFS will be changed to provide the "atime/noatime" mount
         options just as UFS does via PSARC 1998/093 (RFE 4088189).
         The default behaviour will be different from UFS, though:
                 - removeable media:     "noatime" will be default
                 - fixed disks:          "atime" will be default
         The reason for that is the abovementioned behaviour of flash
         devices, which are mostly irrelevant for UFS but a main usage
         scenario for PCFS, and the abovementioned behaviour of FAT
         access timestamps as per the specification.

MAN PAGE CHANGES

         The man page for mount_pcfs(1M) will be changed to describe the
         new mount options "atime"/"noatime" as per above (6581003). The
         additional text will be:

                             atime | noatime
                                 Enable or disable writing  access
                                 timestamps   on   DOS   formatted
                                 media.  Default for  fixed  disks
                                 is  atime,  while  for removeable
                                 media noatime is used. This is so
                                 that  writes to flash-based media
                                 ("memory sticks") can  be  minim-
                                 ized, to prolong lifetime.