Initial root filesystem is now on a ramdisk that is part of the image.

commands/simple/loadramdisk.c

@@ -0,0 +1,126 @@
+/*
+loadramdisk.c
+
+Copy a device or file specified as argument to /dev/ram
+*/
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+
+#define RAM	"/dev/ram"
+
+char buf[10240];
+
+static unsigned long size_device(int fd);
+
+int main(int argc, char *argv[])
+{
+	unsigned long off, size;
+	int r, s, fd, ramfd;
+	char *src;
+
+	if (argc != 2)
+	{
+		fprintf(stderr, "Usage: loadramdisk <file>\n");
+		exit(1);
+	}
+	src= argv[1];
+	fd= open(src, O_RDONLY);
+	if (fd < 0)
+	{
+		fprintf(stderr, "Unable to open '%s': %s\n",
+			src, strerror(errno));
+		exit(1);
+	}
+
+	/* Get the size of the device */
+	errno= 0;
+	size= size_device(fd);
+	if (errno != 0)
+	{
+		fprintf(stderr, "Lseek(end) failed on '%s': %s\n",
+			src, strerror(errno));
+		exit(1);
+	}
+	if (lseek(fd, 0, SEEK_SET) != 0)
+	{
+		fprintf(stderr, "Lseek(0) failed on '%s': %s\n",
+			src, strerror(errno));
+		exit(1);
+	}
+
+	ramfd= open(RAM, O_RDWR);
+	if (ramfd < 0)
+	{
+		fprintf(stderr, "Unable to open '%s': %s\n",
+			RAM, strerror(errno));
+		exit(1);
+	}
+	r= ioctl(ramfd, MIOCRAMSIZE, &size);
+	if (r != 0)
+	{
+		fprintf(stderr, "MIOCRAMSIZE %lu failed on '%s': %s\n",
+			size, RAM, strerror(errno));
+		exit(1);
+	}
+
+	off= 0;
+	while (off < size)
+	{
+		r= read(fd, buf, sizeof(buf));
+		if (r <= 0)
+		{
+			fprintf(stderr, "error reading '%s': %s\n",
+				src, r == 0 ? "unexpected EOF" :
+				strerror(errno));
+			exit(1);
+		}
+		s= write(ramfd, buf, r);
+		if (s != r)
+		{
+			fprintf(stderr, "error writing to '%s': %s\n",
+				s >= 0 ? "short write" : strerror(errno));
+			exit(1);
+		}
+		off += r;
+	}
+	exit(0);
+}
+
+static unsigned long size_device(int fd)
+{
+	char b;
+	int r;
+	unsigned long low, mid, high;
+
+	/* Try to find the size of a device using binary search */
+	low= 0;
+	high= -1;
+
+	while (mid= low+(high-low)/2, mid > low)
+	{
+		if (lseek(fd, mid, SEEK_SET) != mid)
+		{
+			fprintf(stderr, "lseek to %lu failed: %s\n",
+				mid, strerror(errno));
+			exit(1);
+		}
+		r= read(fd, &b, 1);
+		if (r < 0)
+		{
+			fprintf(stderr, "read failed at position %lu: %s\n",
+				mid, strerror(errno));
+			exit(1);
+		}
+		if (r > 0)
+			low= mid;
+		else
+			high= mid;
+	}
+	return high;
+}