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[dm-devel] Re: [PATCH] User-configurable HDIO_GETGEO for dm volumes



Andrew Morton wrote:

Normally kernel functions return zero on success.  So that they can return
negative errno on failure.  Is that appropriate here?  Just propagate the
dm_table_get_geometry() return value?

Fair enough, I've changed the functions to return 0 on success. See the patches attached to the end.

That's brave - we take the hd_geometry straight from userspace without
checking anything?

My original approach didn't work anyway; libdevmapper thinks that a target message is a string and would stop copying at the first null it saw. Since you're also concerned about being locked into a particular hd_geometry structure layout, I respun the patch so that dmsetup passes a string to the dm configuration code; now dm performs some basic range/sanity checks. However, the patch doesn't check that the CHS values make sense or are even close to the real disk size; if somebody in userspace wants to configure a 150G dm device to have the same geometry as a 360K floppy disk, so be it. Geometries seem to be rather inaccurate anyway.

Or, were you worried that I'm dereferencing a userspace pointer in the kernel? The code that calls _setgeo handles that properly.

Will this code dtrt if userspace is 32-bit and the kernel is 64-bit?

There shouldn't be any 32/64 mis-match issues with passing a string. If one tries to pass too-large values, -EINVAL is returned.

> struct hd_geometry looks like something which different compilers could lay
out differently, perhaps even different gcc versions.  We're relying upon
the userspace representation being identical to the kernel's
representation.

It means that struct hd_geometry becomes part of the kernel ABI.  We can
never again change it and neither we (nor the compiler) can ever change its
layout.  That's dangerous.  I'd suggest that you not use hd_geometry in
this way (unless we're already using it that way, which might be the case).

hd_geometry is already part of the kernel ABI because the HDIO_GETGEO ioctl takes a pointer to a struct hd_geometry in userspace and fills it out. Though, now that I've changed the setgeo half to pass a string around, I suppose the point is partially moot.

It'd be better to use some carefully laid-out and documented structure
which is private to DM and which is designed for future-compatibility and
for user<->kernel communication.

--D

Signed-off-by: Darrick J. Wong <djwong us ibm com>
diff -aurp -x '*CVS*' device-mapper-cvs/dmsetup/dmsetup.c device-mapper/dmsetup/dmsetup.c
--- device-mapper-cvs/dmsetup/dmsetup.c	2006-02-03 06:23:22.000000000 -0800
+++ device-mapper/dmsetup/dmsetup.c	2006-02-16 17:10:04.000000000 -0800
@@ -35,6 +35,7 @@
 #include <sys/param.h>
 #include <locale.h>
 #include <langinfo.h>
+#include <linux/hdreg.h>
 
 #ifdef HAVE_SYS_IOCTL_H
 #  include <sys/ioctl.h>
@@ -508,6 +509,49 @@ static int _message(int argc, char **arg
 	return r;
 }
 
+static int _setgeo(int argc, char **argv, void *data)
+{
+	int r = 0, i;
+	struct dm_task *dmt;
+	char *geo = NULL;
+
+	if (!(dmt = dm_task_create(DM_DEVICE_SETGEO)))
+		return 0;
+
+	if (_switches[UUID_ARG] || _switches[MAJOR_ARG]) {
+		if (!_set_task_device(dmt, NULL, 0))
+			goto out;
+	} else {
+		if (!_set_task_device(dmt, argv[1], 0))
+			goto out;
+		argc--;
+		argv++;
+	}
+
+	geo = malloc(strlen(argv[1]) + strlen(argv[2]) +
+		     strlen(argv[3]) + strlen(argv[4]) + 4);
+	if (!geo)
+		goto out;
+
+	r = sprintf(geo, "%s %s %s %s", argv[1], argv[2], argv[3], argv[4]);
+
+	if (!dm_task_set_message(dmt, geo))
+		goto out;
+
+	/* run the task */
+	if (!dm_task_run(dmt))
+		goto out;
+
+	r = 1;
+
+      out:
+	if (geo)
+		free(geo);
+	dm_task_destroy(dmt);
+
+	return r;
+}
+
 static int _version(int argc, char **argv, void *data)
 {
 	char version[80];
@@ -1326,6 +1370,7 @@ static struct command _commands[] = {
 	{"mknodes", "[<device>]", 0, 1, _mknodes},
 	{"targets", "", 0, 0, _targets},
 	{"version", "", 0, 0, _version},
+	{"setgeometry", "<device> <cyl> <head> <sect> <start>", 5, 5, _setgeo},
 	{NULL, NULL, 0, 0, NULL}
 };
 
diff -aurp -x '*CVS*' device-mapper-cvs/kernel/ioctl/dm-ioctl.h device-mapper/kernel/ioctl/dm-ioctl.h
--- device-mapper-cvs/kernel/ioctl/dm-ioctl.h	2005-10-04 13:12:32.000000000 -0700
+++ device-mapper/kernel/ioctl/dm-ioctl.h	2006-02-16 11:46:12.000000000 -0800
@@ -220,6 +220,7 @@ enum {
 	/* Added later */
 	DM_LIST_VERSIONS_CMD,
 	DM_TARGET_MSG_CMD,
+	DM_DEV_SETGEO_CMD
 };
 
 /*
@@ -249,6 +250,7 @@ typedef char ioctl_struct[308];
 #define DM_TABLE_STATUS_32  _IOWR(DM_IOCTL, DM_TABLE_STATUS_CMD, ioctl_struct)
 #define DM_LIST_VERSIONS_32 _IOWR(DM_IOCTL, DM_LIST_VERSIONS_CMD, ioctl_struct)
 #define DM_TARGET_MSG_32    _IOWR(DM_IOCTL, DM_TARGET_MSG_CMD, ioctl_struct)
+#define DM_DEV_SETGEO_32    _IOWR(DM_IOCTL, DM_DEV_SETGEO_CMD, ioctl_struct)
 #endif
 
 #define DM_IOCTL 0xfd
@@ -272,6 +274,7 @@ typedef char ioctl_struct[308];
 #define DM_LIST_VERSIONS _IOWR(DM_IOCTL, DM_LIST_VERSIONS_CMD, struct dm_ioctl)
 
 #define DM_TARGET_MSG	 _IOWR(DM_IOCTL, DM_TARGET_MSG_CMD, struct dm_ioctl)
+#define DM_DEV_SETGEO	 _IOWR(DM_IOCTL, DM_DEV_SETGEO_CMD, struct dm_ioctl)
 
 #define DM_VERSION_MAJOR	4
 #define DM_VERSION_MINOR	5
diff -aurp -x '*CVS*' device-mapper-cvs/lib/ioctl/libdm-iface.c device-mapper/lib/ioctl/libdm-iface.c
--- device-mapper-cvs/lib/ioctl/libdm-iface.c	2006-02-03 06:23:22.000000000 -0800
+++ device-mapper/lib/ioctl/libdm-iface.c	2006-02-14 14:23:16.000000000 -0800
@@ -103,6 +103,9 @@ static struct cmd_data _cmd_data_v4[] = 
 #ifdef DM_TARGET_MSG
 	{"message",	DM_TARGET_MSG,		{4, 2, 0}},
 #endif
+#ifdef DM_DEV_SETGEO
+	{"setgeo",	DM_DEV_SETGEO,		{4, 2, 0}},
+#endif
 };
 /* *INDENT-ON* */
 
diff -aurp -x '*CVS*' device-mapper-cvs/lib/libdevmapper.h device-mapper/lib/libdevmapper.h
--- device-mapper-cvs/lib/libdevmapper.h	2006-02-03 06:23:22.000000000 -0800
+++ device-mapper/lib/libdevmapper.h	2006-02-14 14:04:55.000000000 -0800
@@ -80,7 +80,9 @@ enum {
 
 	DM_DEVICE_LIST_VERSIONS,
 	
-	DM_DEVICE_TARGET_MSG
+	DM_DEVICE_TARGET_MSG,
+
+	DM_DEVICE_SETGEO
 };
 
 struct dm_task;
diff -aurp old/drivers/md/dm.c linux-2.6.16-rc3/drivers/md/dm.c
--- old/drivers/md/dm.c	2006-02-15 10:49:46.000000000 -0800
+++ linux-2.6.16-rc3/drivers/md/dm.c	2006-02-16 10:23:54.000000000 -0800
@@ -17,6 +17,7 @@
 #include <linux/mempool.h>
 #include <linux/slab.h>
 #include <linux/idr.h>
+#include <linux/hdreg.h>
 
 static const char *_name = DM_NAME;
 
@@ -225,6 +226,13 @@ static int dm_blk_close(struct inode *in
 	return 0;
 }
 
+static int dm_blk_getgeo(struct block_device *bdev, struct hd_geometry *geo)
+{
+	struct mapped_device *md = bdev->bd_disk->private_data;
+
+	return dm_table_get_geometry(md->map, geo);
+}	
+
 static inline struct dm_io *alloc_io(struct mapped_device *md)
 {
 	return mempool_alloc(md->io_pool, GFP_NOIO);
@@ -1242,6 +1250,7 @@ int dm_suspended(struct mapped_device *m
 static struct block_device_operations dm_blk_dops = {
 	.open = dm_blk_open,
 	.release = dm_blk_close,
+	.getgeo = dm_blk_getgeo,
 	.owner = THIS_MODULE
 };
 
diff -aurp old/drivers/md/dm.h linux-2.6.16-rc3/drivers/md/dm.h
--- old/drivers/md/dm.h	2006-02-15 10:49:46.000000000 -0800
+++ linux-2.6.16-rc3/drivers/md/dm.h	2006-02-13 17:35:24.000000000 -0800
@@ -123,6 +123,8 @@ void dm_table_resume_targets(struct dm_t
 int dm_table_any_congested(struct dm_table *t, int bdi_bits);
 void dm_table_unplug_all(struct dm_table *t);
 int dm_table_flush_all(struct dm_table *t);
+int dm_table_get_geometry(struct dm_table *t, struct hd_geometry *geo);
+int dm_table_set_geometry(struct dm_table *t, struct hd_geometry *geo);
 
 /*-----------------------------------------------------------------
  * A registry of target types.
diff -aurp old/drivers/md/dm-ioctl.c linux-2.6.16-rc3/drivers/md/dm-ioctl.c
--- old/drivers/md/dm-ioctl.c	2006-02-15 10:49:46.000000000 -0800
+++ linux-2.6.16-rc3/drivers/md/dm-ioctl.c	2006-02-16 11:49:26.000000000 -0800
@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 #include <linux/devfs_fs_kernel.h>
 #include <linux/dm-ioctl.h>
+#include <linux/hdreg.h>
 
 #include <asm/uaccess.h>
 
@@ -690,6 +691,51 @@ static int dev_rename(struct dm_ioctl *p
 	return dm_hash_rename(param->name, new_name);
 }
 
+static int dev_setgeo(struct dm_ioctl *param, size_t param_size)
+{
+	int r = 0, x;
+	size_t len;
+	struct mapped_device *md;
+	struct dm_table *tbl;
+	struct hd_geometry dgm;
+	struct dm_target_msg *tmsg;
+	unsigned long indata[4];
+
+	r = -ENXIO;
+
+	md = find_device(param);
+	if (!md)
+		goto out;
+
+	/*
+	 * Grab our input buffer.
+	 */
+	tmsg = get_result_buffer(param, param_size, &len);
+
+	r = -EINVAL;
+	x = sscanf(tmsg->message, "%lu %lu %lu %lu", indata, indata + 1, indata + 2, indata + 3);
+	if (x != 4)
+		goto out2;
+
+	if (indata[0] > 65535 || indata[1] > 255
+	    || indata[2] > 255 || indata[3] > ULONG_MAX)
+		goto out2;
+
+	dgm.cylinders = indata[0];
+	dgm.heads = indata[1];
+	dgm.sectors = indata[2];
+	dgm.start = indata[3];
+
+	tbl = dm_get_table(md);
+	r = dm_table_set_geometry(tbl, &dgm);
+
+	dm_table_put(tbl);
+out2:
+	dm_put(md);
+out:
+	return r;
+}
+
 static int do_suspend(struct dm_ioctl *param)
 {
 	int r = 0;
@@ -1214,7 +1260,8 @@ static ioctl_fn lookup_ioctl(unsigned in
 
 		{DM_LIST_VERSIONS_CMD, list_versions},
 
-		{DM_TARGET_MSG_CMD, target_message}
+		{DM_TARGET_MSG_CMD, target_message},
+		{DM_DEV_SETGEO_CMD, dev_setgeo}
 	};
 
 	return (cmd >= ARRAY_SIZE(_ioctls)) ? NULL : _ioctls[cmd].fn;
diff -aurp old/drivers/md/dm-table.c linux-2.6.16-rc3/drivers/md/dm-table.c
--- old/drivers/md/dm-table.c	2006-02-15 10:49:46.000000000 -0800
+++ linux-2.6.16-rc3/drivers/md/dm-table.c	2006-02-16 11:43:05.000000000 -0800
@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 #include <linux/interrupt.h>
 #include <asm/atomic.h>
+#include <linux/hdreg.h>
 
 #define MAX_DEPTH 16
 #define NODE_SIZE L1_CACHE_BYTES
@@ -53,6 +54,9 @@ struct dm_table {
 	/* events get handed up using this callback */
 	void (*event_fn)(void *);
 	void *event_context;
+
+	/* forced geometry settings */
+	struct hd_geometry forced_geometry;
 };
 
 /*
@@ -945,6 +949,34 @@ int dm_table_flush_all(struct dm_table *
 	return ret;
 }
 
+int dm_table_get_geometry(struct dm_table *t, struct hd_geometry *geo)
+{
+	sector_t sects;
+
+	sects = t->forced_geometry.cylinders * t->forced_geometry.heads
+		* t->forced_geometry.sectors;
+
+	if (!sects) {
+		return -ENOTTY;
+	}
+
+	memcpy(geo, &t->forced_geometry, sizeof(*geo));
+
+	return 0;
+}
+
+int dm_table_set_geometry(struct dm_table *t, struct hd_geometry *geo)
+{
+	sector_t sz = (sector_t)geo->cylinders * geo->heads * geo->sectors;
+
+	if (geo->start > sz)
+		return -EINVAL;
+
+	memcpy(&t->forced_geometry, geo, sizeof(*geo));
+
+	return 0;
+}
+
 EXPORT_SYMBOL(dm_vcalloc);
 EXPORT_SYMBOL(dm_get_device);
 EXPORT_SYMBOL(dm_put_device);
diff -aurp old/include/linux/compat_ioctl.h linux-2.6.16-rc3/include/linux/compat_ioctl.h
--- old/include/linux/compat_ioctl.h	2006-02-15 10:49:47.000000000 -0800
+++ linux-2.6.16-rc3/include/linux/compat_ioctl.h	2006-02-16 11:48:53.000000000 -0800
@@ -151,6 +151,7 @@ COMPATIBLE_IOCTL(DM_TABLE_DEPS)
 COMPATIBLE_IOCTL(DM_TABLE_STATUS)
 COMPATIBLE_IOCTL(DM_LIST_VERSIONS)
 COMPATIBLE_IOCTL(DM_TARGET_MSG)
+COMPATIBLE_IOCTL(DM_DEV_SETGEO)
 /* Big K */
 COMPATIBLE_IOCTL(PIO_FONT)
 COMPATIBLE_IOCTL(GIO_FONT)
diff -aurp old/include/linux/dm-ioctl.h linux-2.6.16-rc3/include/linux/dm-ioctl.h
--- old/include/linux/dm-ioctl.h	2006-02-15 10:49:47.000000000 -0800
+++ linux-2.6.16-rc3/include/linux/dm-ioctl.h	2006-02-16 11:47:48.000000000 -0800
@@ -218,6 +218,7 @@ enum {
 	/* Added later */
 	DM_LIST_VERSIONS_CMD,
 	DM_TARGET_MSG_CMD,
+	DM_DEV_SETGEO_CMD
 };
 
 /*
@@ -247,6 +248,7 @@ typedef char ioctl_struct[308];
 #define DM_TABLE_STATUS_32  _IOWR(DM_IOCTL, DM_TABLE_STATUS_CMD, ioctl_struct)
 #define DM_LIST_VERSIONS_32 _IOWR(DM_IOCTL, DM_LIST_VERSIONS_CMD, ioctl_struct)
 #define DM_TARGET_MSG_32    _IOWR(DM_IOCTL, DM_TARGET_MSG_CMD, ioctl_struct)
+#define DM_DEV_SETGEO_32    _IOWR(DM_IOCTL, DM_DEV_SETGEO_CMD, ioctl_struct)
 #endif
 
 #define DM_IOCTL 0xfd
@@ -270,6 +272,7 @@ typedef char ioctl_struct[308];
 #define DM_LIST_VERSIONS _IOWR(DM_IOCTL, DM_LIST_VERSIONS_CMD, struct dm_ioctl)
 
 #define DM_TARGET_MSG	 _IOWR(DM_IOCTL, DM_TARGET_MSG_CMD, struct dm_ioctl)
+#define DM_DEV_SETGEO	 _IOWR(DM_IOCTL, DM_DEV_SETGEO_CMD, struct dm_ioctl)
 
 #define DM_VERSION_MAJOR	4
 #define DM_VERSION_MINOR	5

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