bufq(9) [netbsd man page]
BUFQ(9) BSD Kernel Developer's Manual BUFQ(9) NAME
bufq, bufq_state, bufq_alloc, bufq_drain, bufq_free, bufq_getstrategyname, bufq_move, bufq_put, bufq_get, bufq_peek, bufq_cancel -- device buffer queues SYNOPSIS
#include <sys/bufq.h> int bufq_alloc(struct bufq_state **bufq, const char *strategy, int flags); void bufq_drain(struct bufq_state *bufq); void bufq_free(struct bufq_state *bufq); const char * bufq_getstrategyname(struct bufq_state *bufq); void bufq_move(struct bufq_state *dst, struct bufq_state *src); void bufq_put(struct bufq_state *bufq, struct buf *bp); struct buf * bufq_get(struct bufq_state *bufq); struct buf * bufq_peek(struct bufq_state *bufq); struct buf * bufq_cancel(struct bufq_state *bufq, struct buf *bp); DESCRIPTION
The bufq subsystem is a set of operations for the management of device buffer queues. The primary data type for using the operations is the bufq_state structure, which is opaque for users. FUNCTIONS
bufq_alloc(bufq, strategy, flags) Allocate and initialize a bufq_state descriptor. The argument strategy specifies a buffer queue strategy to be used for this buffer queue. The following special values can be used: BUFQ_STRAT_ANY Let bufq_alloc() select a strategy. BUFQ_DISK_DEFAULT_STRAT Let bufq_alloc() select a strategy, assuming it will be used for a normal disk device. Valid bits for the flags are: BUFQ_SORT_RAWBLOCK sort by b_rawblkno BUFQ_SORT_CYLINDER sort by b_cylinder and then by b_rawblkno BUFQ_EXACT Fail if a strategy specified by strategy is not available. In that case, bufq_alloc returns ENOENT. If this flag is not specified, bufq_alloc() will silently use one of available strategies. bufq_drain(bufq) Drain a bufq_state descriptor. bufq_free(bufq) Destroy a bufq_state descriptor. bufq_getstrategyname(bufq) Get a strategy identifier of a buffer queue, the string returned will be NUL-terminated and it always will be a valid strategy name. bufq_move(dst, src) Move all requests from the buffer queue src to the buffer queue dst. bufq_put(bufq, bp) Put the buf bp in the queue. bufq_get(bufq) Get the next buf from the queue and remove it from the queue. Returns NULL if the queue is empty. bufq_peek(bufq) Get the next buf from the queue without removal. The next buf will remain the same until bufq_get(), bufq_put(), or bufq_drain() is called. Returns NULL if the queue is empty. bufq_cancel(bufq, bp) Cancel the buf bp issued earlier on the queue. Returns NULL if the element can not be found on the queue or bp if it has been found and removed. This operation can be computationally expensive if there are a lot of buffers queued. CODE REFERENCES
The actual code implementing the device buffer queues can be found in the file sys/kern/subr_bufq.c. HISTORY
The bufq subsystem appeared in NetBSD 2.0. AUTHORS
The bufq subsystem was written by Jurgen Hannken-Illjes <hannken@NetBSD.org>. BSD
January 24, 2009 BSD
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msgsnap(2) System Calls msgsnap(2) NAME
msgsnap - message queue snapshot operation SYNOPSIS
#include <sys/msg.h> msgsnap(int msqid, void *buf, size_t bufsz, long msgtyp); DESCRIPTION
The msgsnap() function reads all of the messages of type msgtyp from the queue associated with the message queue identifier specified by msqid and places them in the user-defined buffer pointed to by buf. The buf argument points to a user-defined buffer that on return will contain first a buffer header structure: struct msgsnap_head { size_t msgsnap_size; /* bytes used/required in the buffer */ size_t msgsnap_nmsg; /* number of messages in the buffer */ }; followed by msgsnap_nmsg messages, each of which starts with a message header: struct msgsnap_mhead { size_t msgsnap_mlen; /* number of bytes in the message */ long msgsnap_mtype; /* message type */ }; and followed by msgsnap_mlen bytes containing the message contents. Each subsequent message header is located at the first byte following the previous message contents, rounded up to a sizeof(size_t) bound- ary. The bufsz argument specifies the size of buf in bytes. If bufsz is less than sizeof(msgsnap_head), msgsnap() fails with EINVAL. If bufsz is insufficient to contain all of the requested messages, msgsnap() succeeds but returns with msgsnap_nmsg set to 0 and with msgsnap_size set to the required size of the buffer in bytes. The msgtyp argument specifies the types of messages requested as follows: o If msgtyp is 0, all of the messages on the queue are read. o If msgtyp is greater than 0, all messages of type msgtyp are read. o If msgtyp is less than 0, all messages with type less than or equal to the absolute value of msgtyp are read. The msgsnap() function is a non-destructive operation. Upon completion, no changes are made to the data structures associated with msqid. RETURN VALUES
Upon successful completion, msgsnap() returns 0. Otherwise, -1 is returned and errno is set to indicate the error. ERRORS
The msgsnap() function will fail if: EACCES Operation permission is denied to the calling process. See intro(2). EINVAL The msqid argument is not a valid message queue identifier or the value of bufsz is less than sizeof(struct msgsnap_head). EFAULT The buf argument points to an illegal address. USAGE
The msgsnap() function returns a snapshot of messages on a message queue at one point in time. The queue contents can change immediately following return from msgsnap(). EXAMPLES
Example 1: msgsnap() example This is sample C code indicating how to use the msgsnap function (see msgids(2)). void process_msgid(int msqid) { size_t bufsize; struct msgsnap_head *buf; struct msgsnap_mhead *mhead; int i; /* allocate a minimum-size buffer */ buf = malloc(bufsize = sizeof(struct msgsnap_head)); /* read all of the messages from the queue */ for (;;) { if (msgsnap(msqid, buf, bufsize, 0) != 0) { perror("msgsnap"); free(buf); return; } if (bufsize >= buf->msgsnap_size) /* we got them all */ break; /* we need a bigger buffer */ buf = realloc(buf, bufsize = buf->msgsnap_size); } /* process each message in the queue (there may be none) */ mhead = (struct msgsnap_mhead *)(buf + 1); /* first message */ for (i = 0; i < buf->msgsnap_nmsg; i++) { size_t mlen = mhead->msgsnap_mlen; /* process the message contents */ process_message(mhead->msgsnap_mtype, (char *)(mhead+1), mlen); /* advance to the next message header */ mhead = (struct msgsnap_mhead *) ((char *)mhead + sizeof(struct msgsnap_mhead) + ((mlen + sizeof(size_t) - 1) & ~(sizeof(size_t) - 1))); } free(buf); } ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |MT-Level |Async-Signal-Safe | +-----------------------------+-----------------------------+ SEE ALSO
ipcrm(1), ipcs(1), intro(2), msgctl(2), msgget(2), msgids(2), msgrcv(2), msgsnd(2), attributes(5) SunOS 5.10 8 Mar 2000 msgsnap(2)