Introduce OS-dependent stuff

- move GetCommandForPid() into a separate file
- slightly rewrite it to be more readable along the way

src/osdep/linux.c

@@ -0,0 +1,65 @@
+
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include <WINGs/WUtil.h>
+
+#include "../wconfig.h"
+
+/*
+ * copy argc and argv for an existing process identified by `pid'
+ * into suitable storage given in ***argv and *argc.
+ *
+ * returns 0 for failure, in which case argc := 0 and arv := NULL
+ * returns 1 for success
+ */
+Bool GetCommandForPid(int pid, char ***argv, int *argc)
+{
+	static char buf[_POSIX_ARG_MAX];
+	int fd, i, j;
+	ssize_t count;
+
+	*argv = NULL;
+	*argc = 0;
+
+	/* cmdline is a flattened series of null-terminated strings */
+	snprintf(buf, sizeof(buf), "/proc/%d/cmdline", pid);
+	if ((fd = open(buf, O_RDONLY)) == -1)
+		return False;
+
+	/* XXX: read/close errors */
+	if ((count = read(fd, buf, sizeof(buf))) == -1) {
+		close(fd);
+		return False;
+	}
+	close(fd);
+
+	for (i = 0; i < count; i++)
+		if (buf[i] == '\0')
+			(*argc)++;
+
+	if (*argc == 0)
+		return False;
+
+	*argv = (char **)wmalloc(sizeof(char *) * *argc);
+	(*argv)[0] = buf;
+
+	/* go through buf, set argv[$next] to the beginning of each string */
+	for (i = 0, j = 1; i < count; i++) {
+		if (buf[i] != '\0')
+			continue;
+		if (i < count - 1)
+			(*argv)[j++] = &buf[i + 1];
+		if (j == *argc)
+			break;
+	}
+
+	return True;
+}