diff --git a/src/libdisk/disk.c b/src/libdisk/disk.c
new file mode 100644
index 0000000..bb34b65
--- /dev/null
+++ b/src/libdisk/disk.c
@@ -0,0 +1,350 @@
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+#include <ctype.h>
+#include <disk.h>
+
+static Disk*
+mkwidth(Disk *disk)
+{
+	char buf[40];
+
+	sprint(buf, "%lld", disk->size);
+	disk->width = strlen(buf);
+	return disk;
+}
+
+/*
+ * Discover the disk geometry by various sleazeful means.
+ * 
+ * First, if there is a partition table in sector 0,
+ * see if all the partitions have the same end head
+ * and sector; if so, we'll assume that that's the 
+ * right count.
+ * 
+ * If that fails, we'll try looking at the geometry that the ATA
+ * driver supplied, if any, and translate that as a
+ * BIOS might. 
+ * 
+ * If that too fails, which should only happen on a SCSI
+ * disk with no currently defined partitions, we'll try
+ * various common (h, s) pairs used by BIOSes when faking
+ * the geometries.
+ */
+typedef struct Table  Table;
+typedef struct Tentry Tentry;
+struct Tentry {
+	uchar	active;			/* active flag */
+	uchar	starth;			/* starting head */
+	uchar	starts;			/* starting sector */
+	uchar	startc;			/* starting cylinder */
+	uchar	type;			/* partition type */
+	uchar	endh;			/* ending head */
+	uchar	ends;			/* ending sector */
+	uchar	endc;			/* ending cylinder */
+	uchar	xlba[4];			/* starting LBA from beginning of disc */
+	uchar	xsize[4];		/* size in sectors */
+};
+enum {
+	Toffset		= 446,		/* offset of partition table in sector */
+	Magic0		= 0x55,
+	Magic1		= 0xAA,
+	NTentry		= 4,
+};
+struct Table {
+	Tentry	entry[NTentry];
+	uchar	magic[2];
+};
+static int
+partitiongeometry(Disk *disk)
+{
+	char *rawname;
+	int i, h, rawfd, s;
+	uchar buf[512];
+	Table *t;
+
+	t = (Table*)(buf + Toffset);
+
+	/*
+	 * look for an MBR first in the /dev/sdXX/data partition, otherwise
+	 * attempt to fall back on the current partition.
+	 */
+	rawname = malloc(strlen(disk->prefix) + 5);	/* prefix + "data" + nul */
+	if(rawname == nil)
+		return -1;
+
+	strcpy(rawname, disk->prefix);
+	strcat(rawname, "data");
+	rawfd = open(rawname, OREAD);
+	free(rawname);
+	if(rawfd >= 0
+	&& seek(rawfd, 0, 0) >= 0
+	&& readn(rawfd, buf, 512) == 512
+	&& t->magic[0] == Magic0
+	&& t->magic[1] == Magic1) {
+		close(rawfd);
+	} else {
+		if(rawfd >= 0)
+			close(rawfd);
+		if(seek(disk->fd, 0, 0) < 0
+		|| readn(disk->fd, buf, 512) != 512
+		|| t->magic[0] != Magic0
+		|| t->magic[1] != Magic1) {
+			return -1;
+		}
+	}
+
+	h = s = -1;
+	for(i=0; i<NTentry; i++) {
+		if(t->entry[i].type == 0)
+			continue;
+
+		t->entry[i].ends &= 63;
+		if(h == -1) {
+			h = t->entry[i].endh;
+			s = t->entry[i].ends;
+		} else {
+			/*
+			 * Only accept the partition info if every
+			 * partition is consistent.
+			 */
+			if(h != t->entry[i].endh || s != t->entry[i].ends)
+				return -1;
+		}
+	}
+
+	if(h == -1)
+		return -1;
+
+	disk->h = h+1;	/* heads count from 0 */
+	disk->s = s;	/* sectors count from 1 */
+	disk->c = disk->secs / (disk->h*disk->s);
+	disk->chssrc = Gpart;
+	return 0;
+}
+
+/*
+ * If there is ATA geometry, use it, perhaps massaged.
+ */
+static int
+drivergeometry(Disk *disk)
+{
+	int m;
+
+	if(disk->c == 0 || disk->h == 0 || disk->s == 0)
+		return -1;
+
+	disk->chssrc = Gdisk;
+	if(disk->c < 1024)
+		return 0;
+
+	switch(disk->h) {
+	case 15:
+		disk->h = 255;
+		disk->c /= 17;
+		return 0;
+
+	default:
+		for(m = 2; m*disk->h < 256; m *= 2) {
+			if(disk->c/m < 1024) {
+				disk->c /= m;
+				disk->h *= m;
+				return 0;
+			}
+		}
+
+		/* set to 255, 63 and be done with it */
+		disk->h = 255;
+		disk->s = 63;
+		disk->c = disk->secs / (disk->h * disk->s);
+		return 0;
+	}
+	return -1;	/* not reached */
+}
+
+/*
+ * There's no ATA geometry and no partitions.
+ * Our guess is as good as anyone's.
+ */
+static struct {
+	int h;
+	int s;
+} guess[] = {
+	64, 32,
+	64, 63,
+	128, 63,
+	255, 63,
+};
+static int
+guessgeometry(Disk *disk)
+{
+	int i;
+	long c;
+
+	disk->chssrc = Gguess;
+	c = 1024;
+	for(i=0; i<nelem(guess); i++)
+		if(c*guess[i].h*guess[i].s >= disk->secs) {
+			disk->h = guess[i].h;
+			disk->s = guess[i].s;
+			disk->c = disk->secs / (disk->h * disk->s);
+			return 0;
+		}
+
+	/* use maximum values */
+	disk->h = 255;
+	disk->s = 63;
+	disk->c = disk->secs / (disk->h * disk->s);
+	return 0;
+}
+
+static void
+findgeometry(Disk *disk)
+{
+	if(partitiongeometry(disk) < 0
+	&& drivergeometry(disk) < 0
+	&& guessgeometry(disk) < 0) {	/* can't happen */
+		print("we're completely confused about your disk; sorry\n");
+		assert(0);
+	}
+}
+
+static Disk*
+openfile(Disk *disk)
+{
+	Dir *d;
+
+	if((d = dirfstat(disk->fd)) == nil){
+		free(disk);
+		return nil;
+	}
+
+	disk->secsize = 512;
+	disk->size = d->length;
+	disk->secs = disk->size / disk->secsize;
+	disk->offset = 0;
+	free(d);
+
+	findgeometry(disk);
+	return mkwidth(disk);
+}
+
+static Disk*
+opensd(Disk *disk)
+{
+	Biobuf b;
+	char *p, *f[10];
+	int nf;
+
+	Binit(&b, disk->ctlfd, OREAD);
+	while(p = Brdline(&b, '\n')) {
+		p[Blinelen(&b)-1] = '\0';
+		nf = tokenize(p, f, nelem(f));
+		if(nf >= 3 && strcmp(f[0], "geometry") == 0) {
+			disk->secsize = strtoll(f[2], 0, 0);
+			if(nf >= 6) {
+				disk->c = strtol(f[3], 0, 0);
+				disk->h = strtol(f[4], 0, 0);
+				disk->s = strtol(f[5], 0, 0);
+			}
+		}
+		if(nf >= 4 && strcmp(f[0], "part") == 0 && strcmp(f[1], disk->part) == 0) {
+			disk->offset = strtoll(f[2], 0, 0);
+			disk->secs = strtoll(f[3], 0, 0) - disk->offset;
+		}
+	}
+
+	
+	disk->size = disk->secs * disk->secsize;
+	if(disk->size <= 0) {
+		strcpy(disk->part, "");
+		disk->type = Tfile;
+		return openfile(disk);
+	}
+
+	findgeometry(disk);
+	return mkwidth(disk);
+}
+
+Disk*
+opendisk(char *disk, int rdonly, int noctl)
+{
+	char *p, *q;
+	Disk *d;
+
+	d = malloc(sizeof(*d));
+	if(d == nil)
+		return nil;
+
+	d->fd = d->wfd = d->ctlfd = -1;
+	d->rdonly = rdonly;
+
+	d->fd = open(disk, OREAD);
+	if(d->fd < 0) {
+		werrstr("cannot open disk file");
+		free(d);
+		return nil;
+	}
+
+	if(rdonly == 0) {
+		d->wfd = open(disk, OWRITE);
+		if(d->wfd < 0)
+			d->rdonly = 1;
+	}
+
+	if(noctl)
+		return openfile(d);
+
+	p = malloc(strlen(disk) + 4);	/* 4: slop for "ctl\0" */
+	if(p == nil) {
+		close(d->wfd);
+		close(d->fd);
+		free(d);
+		return nil;
+	}
+	strcpy(p, disk);
+
+	/* check for floppy(3) disk */
+	if(strlen(p) >= 7) {
+		q = p+strlen(p)-7;
+		if(q[0] == 'f' && q[1] == 'd' && isdigit(q[2]) && strcmp(q+3, "disk") == 0) {
+			strcpy(q+3, "ctl");
+			if((d->ctlfd = open(p, ORDWR)) >= 0) {
+				*q = '\0';
+				d->prefix = p;
+				d->type = Tfloppy;
+				return openfile(d);
+			}
+		}
+	}
+
+	/* attempt to find sd(3) disk or partition */
+	if(q = strrchr(p, '/'))
+		q++;
+	else
+		q = p;
+
+	strcpy(q, "ctl");
+	if((d->ctlfd = open(p, ORDWR)) >= 0) {
+		*q = '\0';
+		d->prefix = p;
+		d->type = Tsd;
+		d->part = strdup(disk+(q-p));
+		if(d->part == nil){
+			close(d->ctlfd);
+			close(d->wfd);
+			close(d->fd);
+			free(p);
+			free(d);
+			return nil;
+		}
+		return opensd(d);
+	}
+
+	*q = '\0';
+	d->prefix = p;
+	/* assume we just have a normal file */
+	d->type = Tfile;
+	return openfile(d);
+}
+