# read: analogously to write, support reading from in-memory streams in
# addition to file descriptors.
#
# We can pass it either a file descriptor or an address to a stream. If a
# file descriptor is passed in, we _read from it using the right syscall. If a
# stream is passed in (a fake file descriptor), we read from it instead. This
# lets us initialize input for tests.
#
# A little counter-intuitively, the output of 'read' ends up in.. a stream. So
# tests end up doing a redundant copy. Why? Well, consider the alternatives:
#
#   a) Reading into a string, and returning a pointer to the end of the read
#   region, or a count of bytes written. Now this count or end pointer must be
#   managed separately by the caller, which can be error-prone.
#
#   b) Having 'read' return a buffer that it allocates. But there's no way to
#   know in advance how large to make the buffer. If you read less than the
#   size of the buffer you again end up needing to manage initialized vs
#   uninitialized memory.
#
#   c) Creating more helpful variants like 'read-byte' or 'read-until' which
#   also can take a file descriptor or stream, just like 'write'. But such
#   primitives don't exist in the Linux kernel, so we'd be implementing them
#   somehow, either with more internal buffering or by making multiple
#   sysca
/*
 * (C)opyright MMVI Anselm R. Garbe <garbeam at gmail dot com>
 * See LICENSE file for license details.
 */
#include "dwm.h"

#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <unistd.h>

/* static */

static void
bad_malloc(unsigned int size)
{
	fprintf(stderr, "fatal: could not malloc() %d bytes\n",
			(int) size);
	exit(EXIT_FAILURE);
}

/* extern */

void *
emallocz(unsigned int size)
{
	void *res = calloc(1, size);

	if(!res)
		bad_malloc(size);
	return res;
}

void
eprint(const char *errstr, ...) {
	va_list ap;

	va_start(ap, errstr);
	vfprintf(stderr, errstr, ap);
	va_end(ap);
	exit(EXIT_FAILURE);
}

void
spawn(Arg *arg)
{
	char **argv = (char **)arg->argv;

	if(!argv || !argv[0])
		return;
	if(fork() == 0) {
		if(fork() == 0) {
			if(dpy)
				close(ConnectionNumber(dpy));
			setsid();
			execvp(argv[0], argv);
			fprintf(stderr, "dwm: execvp %s", argv[0]);
			perror(" failed");
		}
		exit(EXIT_FAILURE);
	}
	wait(0);
}