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Diffstat (limited to 'sys-utils/ipc.info')
| -rw-r--r-- | sys-utils/ipc.info | 245 |
1 files changed, 119 insertions, 126 deletions
diff --git a/sys-utils/ipc.info b/sys-utils/ipc.info index 5bb1a5383..a1fe498e5 100644 --- a/sys-utils/ipc.info +++ b/sys-utils/ipc.info @@ -1,4 +1,4 @@ -This is ipc.info, produced by makeinfo version 4.0 from ipc.texi. +This is ipc.info, produced by makeinfo version 4.7 from ipc.texi. This file documents the System V style inter process communication primitives available under linux. @@ -16,13 +16,12 @@ END-INFO-DIR-ENTRY File: ipc.info, Node: Top, Next: Overview, Prev: Notes, Up: (dir) -System V IPC. -************* +1 System V IPC. +*************** - These facilities are provided to maintain compatibility with -programs developed on system V unix systems and others that rely on -these system V mechanisms to accomplish inter process communication -(IPC). +These facilities are provided to maintain compatibility with programs +developed on system V unix systems and others that rely on these system +V mechanisms to accomplish inter process communication (IPC). The specifics described here are applicable to the Linux implementation. Other implementations may do things slightly @@ -39,8 +38,8 @@ differently. File: ipc.info, Node: Overview, Next: example, Prev: Top, Up: Top -Overview -======== +1.1 Overview +============ System V IPC consists of three mechanisms: @@ -87,11 +86,11 @@ detailed in the following sections. File: ipc.info, Node: example, Next: perms, Prev: Overview, Up: Overview -example -======= +1.2 example +=========== - Here is a code fragment with pointers on how to use shared memory. -The same methods are applicable to other resources. +Here is a code fragment with pointers on how to use shared memory. The +same methods are applicable to other resources. In a typical access sequence the creator allocates a new instance of the resource with the `get' system call using the IPC_CREAT flag. @@ -103,7 +102,7 @@ creator process: char proc_id = 'C'; int size = 0x5000; /* 20 K */ int flags = 0664 | IPC_CREAT; /* read-only for others */ - + key = ftok ("~creator/ipckey", proc_id); id = shmget (key, size, flags); exit (0); /* quit leaving resource allocated */ @@ -115,19 +114,19 @@ Client process: int id; key_t key; char proc_id = 'C'; - + key = ftok ("~creator/ipckey", proc_id); - + id = shmget (key, 0, 004); /* default size */ if (id == -1) perror ("shmget ..."); - + shmaddr = shmat (id, 0, SHM_RDONLY); /* attach segment for reading */ if (shmaddr == (char *) -1) perror ("shmat ..."); - + local_var = *(shmaddr + 3); /* read segment etc. */ - + shmdt (shmaddr); /* detach segment */ When the resource is no longer needed the creator should remove it. @@ -139,10 +138,10 @@ Creator/owner process 2: File: ipc.info, Node: perms, Next: syscalls, Prev: example, Up: Overview -Permissions -=========== +1.3 Permissions +=============== - Each resource has an associated `ipc_perm' struct which defines the +Each resource has an associated `ipc_perm' struct which defines the creator, owner and access perms for the resource. struct ipc_perm @@ -179,10 +178,10 @@ user. File: ipc.info, Node: syscalls, Next: Messages, Prev: perms, Up: Overview -IPC system calls -================ +1.4 IPC system calls +==================== - This section provides an overview of the IPC system calls. See the +This section provides an overview of the IPC system calls. See the specific sections on each type of resource for details. Each type of mechanism provides a "get", "ctl" and one or more "op" @@ -190,13 +189,13 @@ system calls that allow the user to create or procure the resource (get), define its behaviour or destroy it (ctl) and manipulate the resources (op). -The "get" system calls ----------------------- +1.4.1 The "get" system calls +---------------------------- - The `get' call typically takes a KEY and returns a numeric ID that -is used for further access. The ID is an index into the resource -table. A sequence number is maintained and incremented when a resource -is destroyed so that access using an obsolete ID is likely to fail. +The `get' call typically takes a KEY and returns a numeric ID that is +used for further access. The ID is an index into the resource table. A +sequence number is maintained and incremented when a resource is +destroyed so that access using an obsolete ID is likely to fail. The user also specifies the permissions and other behaviour charecteristics for the current access. The flags are or-ed with the @@ -226,10 +225,10 @@ resource was initialized. It does not imply exclusive access. See Also : *Note msgget::, *Note semget::, *Note shmget::. -The "ctl" system calls ----------------------- +1.4.2 The "ctl" system calls +---------------------------- - Provides or alters the information stored in the structure that +Provides or alters the information stored in the structure that describes the resource indexed by ID. #include <sys/msg.h> @@ -260,10 +259,10 @@ the user to determine or set the values of the semaphores in an array. See Also: *Note msgctl::, *Note semctl::, *Note shmctl::. -The "op" system calls ---------------------- +1.4.3 The "op" system calls +--------------------------- - Used to send or receive messages, read or alter semaphore values, +Used to send or receive messages, read or alter semaphore values, attach or detach shared memory segments. The IPC_NOWAIT flag will cause the operation to fail with error EAGAIN if the process has to wait on the call. @@ -276,10 +275,10 @@ See Also: *Note msgsnd::,*Note msgrcv::,*Note semop::,*Note shmat::, File: ipc.info, Node: Messages, Next: msgget, Prev: syscalls, Up: Top -Messages -======== +1.5 Messages +============ - A message resource is described by a struct `msqid_ds' which is +A message resource is described by a struct `msqid_ds' which is allocated and initialized when the resource is created. Some fields in `msqid_ds' can then be altered (if desired) by invoking `msgctl'. The memory used by the resource is released when it is destroyed by a @@ -328,8 +327,8 @@ this message and free the associated struct `msg'. File: ipc.info, Node: msgget, Next: msgsnd, Prev: Messages, Up: Messages -msgget ------- +1.5.1 msgget +------------ A message queue is allocated by a msgget system call : @@ -367,8 +366,8 @@ ENOMEM : A new `msqid_ds' was to be created but ... nomem. File: ipc.info, Node: msgsnd, Next: msgrcv, Prev: msgget, Up: Messages -msgsnd ------- +1.5.2 msgsnd +------------ int msgsnd (int msqid, struct msgbuf *msgp, int msgsz, int msgflg); @@ -397,8 +396,8 @@ ENOMEM : Could not allocate space for header and text. File: ipc.info, Node: msgrcv, Next: msgctl, Prev: msgsnd, Up: Messages -msgrcv ------- +1.5.3 msgrcv +------------ int msgrcv (int msqid, struct msgbuf *msgp, int msgsz, long msgtyp, int msgflg); @@ -450,8 +449,8 @@ ENOMSG : msg of requested type not found and IPC_NOWAIT specified. File: ipc.info, Node: msgctl, Next: msglimits, Prev: msgrcv, Up: Messages -msgctl ------- +1.5.4 msgctl +------------ int msgctl (int msqid, int cmd, struct msqid_ds *buf); @@ -475,10 +474,8 @@ message queue beyond MSGMNB. incremented and all waiting readers and writers are awakened. These processes will then return with `errno' set to EIDRM. -Errors: - -EPERM : Insufficient privilege to increase the size of the queue -(IPC_SET) or remove it (IPC_RMID). +Errors: EPERM : Insufficient privilege to increase the size of the +queue (IPC_SET) or remove it (IPC_RMID). EACCES : Do not have permission for reading the queue (IPC_STAT). EFAULT : buf not accessible (IPC_STAT, IPC_SET). EIDRM : msg queue was removed. @@ -487,8 +484,8 @@ EINVAL : invalid cmd, msqid < 0 or unused. File: ipc.info, Node: msglimits, Next: Semaphores, Prev: msgctl, Up: Messages -Limis on Message Resources --------------------------- +1.5.5 Limis on Message Resources +-------------------------------- Sizeof various structures: msqid_ds 52 /* 1 per message queue .. dynamic */ @@ -515,11 +512,11 @@ MSGPOOL total size in bytes of msg pool. File: ipc.info, Node: Semaphores, Next: semget, Prev: msglimits, Up: Top -Semaphores -========== +1.6 Semaphores +============== - Each semaphore has a value >= 0. An id provides access to an array -of `nsems' semaphores. Operations such as read, increment or decrement +Each semaphore has a value >= 0. An id provides access to an array of +`nsems' semaphores. Operations such as read, increment or decrement semaphores in a set are performed by the `semop' call which processes `nsops' operations at a time. Each operation is specified in a struct `sembuf' described below. The operations are applied only if all of @@ -565,8 +562,8 @@ Each semaphore is described internally by : File: ipc.info, Node: semget, Next: semop, Prev: Semaphores, Up: Semaphores -semget ------- +1.6.1 semget +------------ A semaphore array is allocated by a semget system call: @@ -611,8 +608,8 @@ EACCES : (procure) do not have permission for specified access. File: ipc.info, Node: semop, Next: semctl, Prev: semget, Up: Semaphores -semop ------ +1.6.2 semop +----------- Operations on semaphore arrays are performed by calling semop : @@ -676,8 +673,8 @@ ERANGE : sem_op + semval > SEMVMX for some operation. File: ipc.info, Node: semctl, Next: semlimits, Prev: semop, Up: Semaphores -semctl ------- +1.6.3 semctl +------------ int semctl (int semid, int semnum, int cmd, union semun arg); @@ -721,9 +718,7 @@ The last two operate on all semaphores in the set. * IPC_SET : sem_perm.uid, sem_perm.gid, sem_perm.mode are updated from user supplied values. -Errors: - -EACCES : do not have permission for specified access. +Errors: EACCES : do not have permission for specified access. EFAULT : arg is not accessible. EIDRM : The resource was removed. EINVAL : semid < 0 or semnum < 0 or semnum >= nsems. @@ -733,8 +728,8 @@ ERANGE : arg.array[i].semval > SEMVMX or < 0 for some i. File: ipc.info, Node: semlimits, Next: Shared Memory, Prev: semctl, Up: Semaphores -Limits on Semaphore Resources ------------------------------ +1.6.4 Limits on Semaphore Resources +----------------------------------- Sizeof various structures: semid_ds 44 /* 1 per semaphore array .. dynamic */ @@ -767,10 +762,10 @@ SEMUME maximum number of undo entries per process. File: ipc.info, Node: Shared Memory, Next: shmget, Prev: semlimits, Up: Top -Shared Memory -============= +1.7 Shared Memory +================= - Shared memory is distinct from the sharing of read-only code pages or +Shared memory is distinct from the sharing of read-only code pages or the sharing of unaltered data pages that is available due to the copy-on-write mechanism. The essential difference is that the shared pages are dirty (in the case of Shared memory) and can be made to @@ -805,8 +800,8 @@ calling shmctl with IPC_RMID. File: ipc.info, Node: shmget, Next: shmat, Prev: Shared Memory, Up: Shared Memory -shmget ------- +1.7.1 shmget +------------ A shared memory segment is allocated by a shmget system call: @@ -853,8 +848,8 @@ ENOMEM : (allocate) Could not allocate memory for shmid_ds or pg_table. File: ipc.info, Node: shmat, Next: shmdt, Prev: shmget, Up: Shared Memory -shmat ------ +1.7.2 shmat +----------- Maps a shared segment into the process' address space. @@ -905,8 +900,8 @@ ENOMEM : Could not allocate memory for descriptor or page tables. File: ipc.info, Node: shmdt, Next: shmctl, Prev: shmat, Up: Shared Memory -shmdt ------ +1.7.3 shmdt +----------- int shmdt (char *shmaddr); @@ -925,8 +920,8 @@ EINVAL : No shared memory segment attached at shmaddr. File: ipc.info, Node: shmctl, Next: shmlimits, Prev: shmdt, Up: Shared Memory -shmctl ------- +1.7.4 shmctl +------------ Destroys allocated segments. Reads/Writes the control structures. @@ -962,8 +957,8 @@ EPERM : not creator, owner or super-user (IPC_SET, IPC_RMID). File: ipc.info, Node: shmlimits, Next: Notes, Prev: shmctl, Up: Shared Memory -Limits on Shared Memory Resources ---------------------------------- +1.7.5 Limits on Shared Memory Resources +--------------------------------------- Limits: * SHMMNI max num of shared segments system wide ... 4096. @@ -977,23 +972,22 @@ Limits: * SHMLBA segment low boundary address multiple. Must be page aligned. SHMLBA = PAGE_SIZE. - -Unused or unimplemented: + Unused or unimplemented: SHMSEG : maximum number of shared segments per process. File: ipc.info, Node: Notes, Next: Top, Prev: shmlimits, Up: Top -Miscellaneous Notes -=================== +1.8 Miscellaneous Notes +======================= - The system calls are mapped into one - `sys_ipc'. This should be +The system calls are mapped into one - `sys_ipc'. This should be transparent to the user. -Semaphore `undo' requests -------------------------- +1.8.1 Semaphore `undo' requests +------------------------------- - There is one sem_undo structure associated with a process for each +There is one sem_undo structure associated with a process for each semaphore which was altered (with an undo request) by the process. `sem_undo' structures are freed only when the process exits. @@ -1008,13 +1002,12 @@ applied with the IPC_NOWAIT flag in effect? Currently those undo operations which go through immediately are applied and those that require a wait are ignored silently. -Shared memory, `malloc' and the `brk'. --------------------------------------- +1.8.2 Shared memory, `malloc' and the `brk'. +-------------------------------------------- - Note that since this section was written the implementation was -changed so that non-specific attaches are done in the region 1G - 1.5G. -However much of the following is still worth thinking about so I left -it in. +Note that since this section was written the implementation was changed +so that non-specific attaches are done in the region 1G - 1.5G. However +much of the following is still worth thinking about so I left it in. On many systems, the shared memory is allocated in a special region of the address space ... way up somewhere. As mentioned earlier, this @@ -1048,11 +1041,11 @@ what is really a shared memory region. For example in the case of a read-only attach, you will not be able to write to the overlapped portion. -Fork, exec and exit -------------------- +1.8.3 Fork, exec and exit +------------------------- - On a fork, the child inherits attached shared memory segments but -not the semaphore undo information. +On a fork, the child inherits attached shared memory segments but not +the semaphore undo information. In the case of an exec, the attached shared segments are detached. The sem undo information however remains intact. @@ -1061,11 +1054,11 @@ The sem undo information however remains intact. adjust values in the undo structures are added to the relevant semvals if the operations are permitted. Disallowed operations are ignored. -Other Features --------------- +1.8.4 Other Features +-------------------- - These features of the current implementation are likely to be -modified in the future. +These features of the current implementation are likely to be modified +in the future. The SHM_LOCK and SHM_UNLOCK flag are available (super-user) for use with the `shmctl' call to prevent swapping of a shared segment. The user @@ -1088,27 +1081,27 @@ And more thanks to Bruno. Tag Table: Node: Top469 -Node: Overview1170 -Node: example3004 -Node: perms4506 -Node: syscalls6066 -Node: Messages9519 -Node: msgget11554 -Node: msgsnd12938 -Node: msgrcv13906 -Node: msgctl15605 -Node: msglimits16814 -Node: Semaphores17691 -Node: semget19650 -Node: semop21203 -Node: semctl23767 -Node: semlimits25526 -Node: Shared Memory26668 -Node: shmget28153 -Node: shmat29948 -Node: shmdt31985 -Node: shmctl32518 -Node: shmlimits33649 -Node: Notes34298 +Node: Overview1171 +Node: example3013 +Node: perms4490 +Node: syscalls6055 +Node: Messages9540 +Node: msgget11580 +Node: msgsnd12976 +Node: msgrcv13956 +Node: msgctl15667 +Node: msglimits16887 +Node: Semaphores17776 +Node: semget19740 +Node: semop21305 +Node: semctl23881 +Node: semlimits25651 +Node: Shared Memory26805 +Node: shmget28295 +Node: shmat30102 +Node: shmdt32151 +Node: shmctl32696 +Node: shmlimits33839 +Node: Notes34502 End Tag Table |