A_MDEV Removal [PSARC/2007/675 FastTrack timeout 12/17/2007]

[Timothy Haley]

I'm re-submitting the specification for PSARC/2007/675.  I think it 
probably would still qualify for self-review, but will go ahead and 
start it as a normal fast-track, to allow for any further comment.

I am sponsoring this case on behalf of Rich Morris.  This case removes
the A_MDEV file system attribute from the set of attributes returned
from fgetattr(3c).  The mounted file system device that this attribute
is returning is available from stat(2) in st_dev.

This case seeks Minor binding, which is the same as the binding for
PSARC 2007/315 "Extensible Attribute Interfaces" which first
introduced the attribute.

Template Version: @(#)sac_nextcase 1.64 07/13/07 SMI
This information is Copyright 2007 Sun Microsystems
1. Introduction
    1.1. Project/Component Working Name:
         A_MDEV removal
    1.2. Name of Document Author/Supplier:
         Author:  Rich Morris
    1.3  Date of This Document:
         6 December, 2007
4. Technical Description

PSARC 2007/315 (Extensible Attribute Interfaces) was approved on
13 June, 2007, and introduced a set of optional system-level file
attributes.  The A_MDEV attribute is one of the system attributes.
This attribute represents the mounted file system device which is
also returned by the stat(2) system call in st_dev.

This value was included in the SUNWattr_ro extended attribute file
for completeness.  However, the mount device is a 32 bit value on
a 32 bit system and a 64 bit value on 64 bit system.  fgetattr(3c)
could be extended to provide both A_MDEV32 and A_MDEV64 attrs in
the returned nvlist.  However, this would require support for 32
bit applications to convert a 32 bit dev_t to and from a 64 bit
dev_t.  Also, for an NFS remote file, fgetattr(3c) will not return
the mount device of the NFS mount, but of the file system on the
server.  That is not the same value returned by stat(2) in st_dev.

Therefore, A_MDEV will be removed from SUNWattr_ro and will not be
returned by fgetattr(3c).  Applications should continue to obtain
the mount device using stat(2).

The changes originally approved by PSARC 2007/315 (Extensible Attribute
Interfaces) were putback into Solaris Nevada on 25 October 2007.

Section 4.1.1 of PSARC 2007/315 shows 2 attributes in XATTR_VIEW_READONLY:

          View                  Attribute               Data type
          XATTR_VIEW_READONLY   A_FSID                  uint64_t
                                A_MDEV                  uint16_t

A_AV_SCANSTAMP was added to XATTR_VIEW_READONLY by PSARC/2007/118 and
A_OPAQUE was added to this view by PSARC/2007/476.  This case removes
A_MDEV so XATTR_VIEW_READONLY now has 3 attributes:

         View                  Attribute               Data type
         XATTR_VIEW_READONLY   A_FSID                  uint64_t
                               A_AV_SCANSTAMP          uint8_array[]
                               A_OPAQUE                boolean_value


6. Resources and Schedule
    6.4. Steering Committee requested information
        6.4.1. Consolidation C-team Name:
                ON
    6.5. ARC review type: Automatic
    6.6. ARC Exposure: open