Kernel Semaphore (KSEM)

>> Intra-Process serialisation mutex KSEM imbedded in the PTDA.
>> This KSEM is sometimes referred to as "fscrit" (file system critical
>> section) since it is used to serialise file system activity within
>> a process.
.p#
 Slot  Pid  Ppid Csid Ord  Sta Pri  pTSD     pPTDA    pTCB     Disp SG Name
*000c# 0002 0000 0002 0004 blk 0804 ab78d000 ab997020 ab978420 1c9c 00 cntrl
##.d ksem %ab997020 +ptda_ptdasem-ptda_start
Signature     : KSEM                        Nest: 0000
Type          : MUTEX
Flags         : 00
Owner         : 0000              PendingWriters: 0000
##


>> MFT Shared KSEM imbedded at the beginning of the MFT

##..d sft d0:8
      sf_ref_count: 0001                        sfi_mode: 00a0
        sf_usercnt: 0000                        sfi_hVPB: 0012
          reserved: 00                         sfi_ctime: 0000
       sf_flags(2): 0100:0000                  sfi_cdate: 0000
         sf_devptr: #0000:0000                 sfi_atime: 0000
            sf_FSC: #00c8:0008                 sfi_adate: 0000
          sf_chain: #0000:0000                 sfi_mtime: 0000
            sf_MFT: fe7fb788                   sfi_mdate: 0000
sfdFAT_firFILEclus: 5ad6                        sfi_size: 000bb135
    sfdFAT_cluspos: 09c8                    sfi_position: 00085d90


##.d ksem %fe7fb788
Signature     : KSEM                        Nest: 0000
Type          : SHARE                    Readers: 0000
Flags         : 01                PendingReaders: 0000
Owner         : 0000              PendingWriters: 0000
##

>> Slot 49 is blocked. So we proceed by finding out what the BlockId
>> represents by finding its owner.

##.pb 49
 Slot  Sta BlockID  Name     Type        Addr    Symbol
 0049  blk fe83bdf4 warp_d

##.m  %0fe83bdf4

*har     par      cpg        va    flg next prev link hash hob   hal
 072c %feaf8dd2 00000400 %00540000 149 072d 072b 0003 0000 0003 0025 hptda=0878
 hal=0025 pal=%ffe5d140  har=072c  hptda=0878  pgoff=00000  f=021
 har     par      cpg        va    flg next prev link hash hob   hal
 0003 %feaef04c 00000400 %fe6ef000 001 0002 0023 0000 0000 0003 0000      =0000
 hob   har hobnxt flgs own  hmte  sown,cnt lt st xf
 0003  072c fec5  1000 ffec 0000  0000 00  01 00 00 vmkrhrw
   pvmli    cs    eip     phlock   cpg      va    flg  hptda hob sig  csig
 %fe82e4c4 002d 0a6800a5 %ac22403c 0001 %fe83c000 0005 024b 0003 ea9f ea9f

>> Block Id is in the kernel resident heap - assume that it is at the
>> beginning of a data portion of a heap block.
>> Dump the header.

##dd  %0fe83bdf4-10 l8
%fe83bde4  00000000 bd100000 fe83fe83 ff7e0018
%fe83bdf4  4d45534b 000a0004 46380001 bd28a801

>> Object Owner Id is ff7e
##.mo ff7e
ff7e ksem
##.d ksem %0fe83bdf4
Signature     : KSEM
Type          : EVENT
Flags         : 04
Owner         : 000a              PendingWriters: 0001
##

Notes:

KSEMs are usually found imbedded in system control blocks for serialisation and sharing purposes.

Dynamically allocated KSEMs are allocated out of one of the kernel heaps.

Virtual Device Driver semaphore helper services result in KSEMs.

Under the ALLSTRICT kernel only, the KSEM has a signature field. This is manufactured by the .D command for non-ALLSTRICT kernels. Under the ALLSTRICT kernel the presence of a KSEM may be verified by dumping the KSEM in bytes. Offset +0x0 is where the signature is located.

The owner field refers to the slot number of the semaphore owner.

When a thread blocks on a KSEM the following addresses are used as the BlockId

MUTEX KSEM

Address of the beginning of the KSEM structure.
SHARED KSEM
Address of the Pending Readers count field within the KSEM structure.
EXCLUSIVE KSEM
Address of the Pending Writers count field within the KSEM structure.
To format KSEM from a BlockId, locate the beginning of the KSEM, either by dumping a few bytes before the BlockId addess. The signature will be visible under the ALLSTICT kernel, which is at the beginning of the KSEM. If the KSEM is allocated from one of the Kernel's heaps then the KSEM object id, 0xff7e will occur in the heap header which prefixes the beginning of the KSEM.

For a description of the KSEM structure see the Kernel Semaphore Structure in the System Reference.