Function pipespace_new

freebsd/kern/sys_pipe.c:537–597

* Allocate kva for pipe circular buffer, the space is pageable * This routine will 'realloc' the size of a pipe safely, if it fails * it will retain the old buffer. * If it fails it will return ENOMEM. */

 * If it fails it will return ENOMEM.
 */
static int
pipespace_new(struct pipe *cpipe, int size)
{
	caddr_t buffer;
	int error, cnt, firstseg;
	static int curfail = 0;
	static struct timeval lastfail;

	KASSERT(!mtx_owned(PIPE_MTX(cpipe)), ("pipespace: pipe mutex locked"));
	KASSERT(!(cpipe->pipe_state & PIPE_DIRECTW),
		("pipespace: resize of direct writes not allowed"));
retry:
	cnt = cpipe->pipe_buffer.cnt;
	if (cnt > size)
		size = cnt;

	size = round_page(size);
	buffer = (caddr_t) vm_map_min(pipe_map);

	error = vm_map_find(pipe_map, NULL, 0, (vm_offset_t *)&buffer, size, 0,
	    VMFS_ANY_SPACE, VM_PROT_RW, VM_PROT_RW, 0);
	if (error != KERN_SUCCESS) {
		if (cpipe->pipe_buffer.buffer == NULL &&
		    size > SMALL_PIPE_SIZE) {
			size = SMALL_PIPE_SIZE;
			pipefragretry++;
			goto retry;
		}
		if (cpipe->pipe_buffer.buffer == NULL) {
			pipeallocfail++;
			if (ppsratecheck(&lastfail, &curfail, 1))
				printf("kern.ipc.maxpipekva exceeded; see tuning(7)\n");
		} else {
			piperesizefail++;
		}
		return (ENOMEM);
	}

	/* copy data, then free old resources if we're resizing */
	if (cnt > 0) {
		if (cpipe->pipe_buffer.in <= cpipe->pipe_buffer.out) {
			firstseg = cpipe->pipe_buffer.size - cpipe->pipe_buffer.out;
			bcopy(&cpipe->pipe_buffer.buffer[cpipe->pipe_buffer.out],
				buffer, firstseg);
			if ((cnt - firstseg) > 0)
				bcopy(cpipe->pipe_buffer.buffer, &buffer[firstseg],
					cpipe->pipe_buffer.in);
		} else {
			bcopy(&cpipe->pipe_buffer.buffer[cpipe->pipe_buffer.out],
				buffer, cnt);
		}
	}
	pipe_free_kmem(cpipe);
	cpipe->pipe_buffer.buffer = buffer;
	cpipe->pipe_buffer.size = size;
	cpipe->pipe_buffer.in = cnt;
	cpipe->pipe_buffer.out = 0;
	cpipe->pipe_buffer.cnt = cnt;