From: Jan Engelhardt <jengelh@...>
Subject: [code] Unlimited partitions, a try
Date: Oct 5, 7:50 am 2007

15 partitions (at least for sd_mod devices) are too few.

So I tried the following: after scanning the disk (sda), when we know
the number of partitions P on a disk, create a new block device
/dev/gd0 that is a copy of sda (in terms of disk->queue, etc.). This
is done using alloc_disk(P).

However, read() on gd0 will just return 0. It takes a `blockdev --rereadpt
/dev/gd0` before the disk is accessible. And if I add a call to
rescan inside gpdisk_new() it oopses (probably rightfully so). I do not 
know all the block layer magic, so expect some horrible code.

Ideas, hints, anything is welcome.

---
 block/Makefile        |    1 
 block/genhd.c         |    5 +
 block/gpdisk.c        |  139 ++++++++++++++++++++++++++++++++++++++++++++++++++
 drivers/scsi/sd.c     |    1 
 fs/partitions/check.c |   19 ++++++
 include/linux/genhd.h |   16 +++++
 include/scsi/sd.h     |    3 +
 7 files changed, 182 insertions(+), 2 deletions(-)

Index: linux-2.6.23/block/Makefile
===================================================================
--- linux-2.6.23.orig/block/Makefile
+++ linux-2.6.23/block/Makefile
@@ -3,6 +3,7 @@
 #
 
 obj-$(CONFIG_BLOCK) := elevator.o ll_rw_blk.o ioctl.o genhd.o scsi_ioctl.o
+obj-${CONFIG_BLOCK} += gpdisk.o
 
 obj-$(CONFIG_BLK_DEV_BSG)	+= bsg.o
 obj-$(CONFIG_IOSCHED_NOOP)	+= noop-iosched.o
Index: linux-2.6.23/block/genhd.c
===================================================================
--- linux-2.6.23.orig/block/genhd.c
+++ linux-2.6.23/block/genhd.c
@@ -744,6 +744,9 @@ struct gendisk *alloc_disk_node(int mino
 		rand_initialize_disk(disk);
 		INIT_WORK(&disk->async_notify,
 			media_change_notify_thread);
+		atomic_set(&disk->gpdisk_enabled, false);
+		disk->gpdisk         = NULL;
+		disk->gpdisk_parent  = NULL;
 	}
 	return disk;
 }
@@ -793,6 +796,8 @@ EXPORT_SYMBOL(set_device_ro);
 void set_disk_ro(struct gendisk *disk, int flag)
 {
 	int i;
+	if (gpdisk_online(disk))
+		set_disk_ro(disk->gpdisk, flag);
 	disk->policy = flag;
 	for (i = 0; i < disk->minors - 1; i++)
 		if (disk->part[i]) disk->part[i]->policy = flag;
Index: linux-2.6.23/block/gpdisk.c
===================================================================
--- /dev/null
+++ linux-2.6.23/block/gpdisk.c
@@ -0,0 +1,139 @@
+#include <linux/genhd.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/idr.h>
+#define MINOR_IS_ALLOCATED ((void *)0xB4C4)
+
+static unsigned int gpdisk_major = 0;
+module_param(gpdisk_major, uint, S_IRUGO);
+
+static LIST_HEAD(gpdisk_regions);
+static DEFINE_SPINLOCK(gpdisk_region_lock);
+static DEFINE_SPINLOCK(gpdisk_id_lock);
+static DEFINE_IDR(gpdisk_id_idr);
+
+static unsigned int gpdisk_first_minor = 0;
+
+static int gpdisk_get_region(unsigned int size)
+{
+	/* still to be done */
+	unsigned int old;
+
+	old = gpdisk_first_minor;
+	gpdisk_first_minor += size;
+	return old;
+}
+
+static void gpdisk_put_region(unsigned int start, unsigned int n)
+{
+	/* same */
+}
+
+static int gpdisk_get_diskid(void)
+{
+	int new_id, ret;
+
+ again:
+	ret = idr_pre_get(&gpdisk_id_idr, GFP_KERNEL);
+	if (ret == 0)
+		return -ENOMEM;
+
+	spin_lock(&gpdisk_id_lock);
+	ret = idr_get_new(&gpdisk_id_idr, MINOR_IS_ALLOCATED, &new_id);
+	if (ret == -EAGAIN) {
+		spin_unlock(&gpdisk_id_lock);
+		cond_resched();
+		goto again;
+	}
+	if (ret != 0)
+		goto out;
+
+	ret = new_id;
+ out:
+	spin_unlock(&gpdisk_id_lock);
+	return ret;
+}
+
+static void gpdisk_put_diskid(unsigned int id)
+{
+	idr_remove(&gpdisk_id_idr, id);
+}
+
+void gpdisk_new(struct gendisk *disk, unsigned int minors)
+{
+	struct block_device *bdev;
+	struct gendisk *gpdisk;
+	int disk_id, minor_start;
+
+	gpdisk = alloc_disk(minors);
+	if (gpdisk == NULL)
+		return;
+
+	disk_id = gpdisk_get_diskid();
+	if (disk_id < 0)
+		goto out;
+
+	minor_start = gpdisk_get_region(minors);
+	if (minor_start < 0)
+		goto out2;
+
+	disk->gpdisk          = gpdisk;
+	disk->gpdisk_id       = disk_id;
+
+	sprintf(gpdisk->disk_name, "gd%u", disk_id);
+	gpdisk->gpdisk_parent = disk;
+	gpdisk->major         = gpdisk_major;
+	gpdisk->first_minor   = minor_start;
+	gpdisk->minors        = minors;
+	gpdisk->fops          = disk->fops;
+
+	/* safe? */
+	gpdisk->private_data  = disk->private_data;
+	gpdisk->queue         = disk->queue;
+	gpdisk->driverfs_dev  = disk->driverfs_dev;
+	gpdisk->flags         = disk->flags;
+
+	add_disk(gpdisk);
+	return;
+
+ out2:
+	gpdisk_put_diskid(disk_id);
+ out:
+	put_disk(gpdisk);
+	return;
+}
+
+void gpdisk_release(struct gendisk *disk)
+{
+	gpdisk_put_region(disk->gpdisk->first_minor, disk->gpdisk->minors);
+	gpdisk_put_diskid(disk->gpdisk_id);
+}
+
+static int __init gpdisk_init(void)
+{
+	int i;
+
+	i = register_blkdev(gpdisk_major, "gpdisk");
+	if (gpdisk_major == 0) {
+		/* dynamic major */
+		if (i == 0)
+			return -ENODEV;
+		gpdisk_major = i;
+	} else {
+		/* fixed major */
+		if (i != 0)
+			return -ENODEV;
+	}
+
+	return 0;
+}
+
+static void __exit gpdisk_exit(void)
+{
+	unregister_blkdev(gpdisk_major, "gpdisk");
+}
+
+module_init(gpdisk_init);
+module_exit(gpdisk_exit);
Index: linux-2.6.23/drivers/scsi/sd.c
===================================================================
--- linux-2.6.23.orig/drivers/scsi/sd.c
+++ linux-2.6.23/drivers/scsi/sd.c
@@ -1610,6 +1610,7 @@ static int sd_probe(struct device *dev)
 	gd = alloc_disk(16);
 	if (!gd)
 		goto out_free;
+	atomic_set(&gd->gpdisk_enabled, true);
 
 	if (!idr_pre_get(&sd_index_idr, GFP_KERNEL))
 		goto out_put;
Index: linux-2.6.23/fs/partitions/check.c
===================================================================
--- linux-2.6.23.orig/fs/partitions/check.c
+++ linux-2.6.23/fs/partitions/check.c
@@ -168,7 +168,7 @@ check_partition(struct gendisk *hd, stru
 	if (isdigit(state->name[strlen(state->name)-1]))
 		sprintf(state->name, "p");
 
-	state->limit = hd->minors;
+	state->limit = MAX_PART;
 	i = res = err = 0;
 	while (!res && check_part[i]) {
 		memset(&state->parts, 0, sizeof(state->parts));
@@ -528,6 +528,7 @@ exit:
 int rescan_partitions(struct gendisk *disk, struct block_device *bdev)
 {
 	struct parsed_partitions *state;
+	unsigned int max;
 	int p, res;
 
 	if (bdev->bd_part_count)
@@ -536,6 +537,11 @@ int rescan_partitions(struct gendisk *di
 	if (res)
 		return res;
 	bdev->bd_invalidated = 0;
+	if (gpdisk_online(disk)) {
+		gpdisk_release(disk);
+		del_gendisk(disk->gpdisk);
+		disk->gpdisk = NULL;
+	}
 	for (p = 1; p < disk->minors; p++)
 		delete_partition(disk, p);
 	if (disk->fops->revalidate_disk)
@@ -544,7 +550,8 @@ int rescan_partitions(struct gendisk *di
 		return 0;
 	if (IS_ERR(state))	/* I/O error reading the partition table */
 		return -EIO;
-	for (p = 1; p < state->limit; p++) {
+	max = min(disk->minors, state->next);
+	for (p = 1; p < max; p++) {
 		sector_t size = state->parts[p].size;
 		sector_t from = state->parts[p].from;
 		if (!size)
@@ -560,6 +567,8 @@ int rescan_partitions(struct gendisk *di
 #endif
 	}
 	kfree(state);
+	if (atomic_read(&disk->gpdisk_enabled) > 0)
+		gpdisk_new(disk, state->next);
 	return 0;
 }
 
@@ -588,6 +597,12 @@ void del_gendisk(struct gendisk *disk)
 {
 	int p;
 
+	if (gpdisk_online(disk)) {
+		gpdisk_release(disk);
+		del_gendisk(disk->gpdisk);
+		disk->gpdisk = NULL;
+	}
+
 	/* invalidate stuff */
 	for (p = disk->minors - 1; p > 0; p--) {
 		invalidate_partition(disk, p);
Index: linux-2.6.23/include/linux/genhd.h
===================================================================
--- linux-2.6.23.orig/include/linux/genhd.h
+++ linux-2.6.23/include/linux/genhd.h
@@ -67,6 +67,7 @@ struct partition {
 #include <linux/string.h>
 #include <linux/fs.h>
 #include <linux/workqueue.h>
+#include <asm/atomic.h>
 
 struct partition {
 	unsigned char boot_ind;		/* 0x80 - active */
@@ -141,6 +142,10 @@ struct gendisk {
 	struct disk_stats dkstats;
 #endif
 	struct work_struct async_notify;
+
+	struct gendisk *gpdisk, *gpdisk_parent;
+	unsigned int gpdisk_id;
+	atomic_t gpdisk_enabled;
 };
 
 /* Structure for sysfs attributes on block devices */
@@ -255,11 +260,22 @@ static inline sector_t get_capacity(stru
 {
 	return disk->capacity;
 }
+
+static inline bool gpdisk_online(const struct gendisk *disk)
+{
+	return atomic_read(&disk->gpdisk_enabled) > 0 && disk->gpdisk != NULL;
+}
+
 static inline void set_capacity(struct gendisk *disk, sector_t size)
 {
 	disk->capacity = size;
+	if (gpdisk_online(disk))
+		disk->gpdisk->capacity = size;
 }
 
+extern void gpdisk_new(struct gendisk *, unsigned int);
+extern void gpdisk_release(struct gendisk *);
+
 #endif  /*  __KERNEL__  */
 
 #ifdef CONFIG_SOLARIS_X86_PARTITION
Index: linux-2.6.23/include/scsi/sd.h
===================================================================
--- linux-2.6.23.orig/include/scsi/sd.h
+++ linux-2.6.23/include/scsi/sd.h
@@ -62,6 +62,9 @@ static void sd_print_sense_hdr(struct sc
 static void sd_print_result(struct scsi_disk *, int);
 
 #define sd_printk(prefix, sdsk, fmt, a...)				\
+	gpdisk_online((sdsk)->disk) ?					\
+	sdev_printk(prefix, (sdsk)->device, "[%s] " fmt,		\
+		    (sdsk)->disk->gpdisk->disk_name, ##a) :		\
         (sdsk)->disk ?							\
 	sdev_printk(prefix, (sdsk)->device, "[%s] " fmt,		\
 		    (sdsk)->disk->disk_name, ##a) :			\
-


From: H. Peter Anvin <hpa@...>
Subject: Re: [code] Unlimited partitions, a try
Date: Oct 5, 6:11 pm 2007

Jan Engelhardt wrote:
> 15 partitions (at least for sd_mod devices) are too few.

Now when we have 20-bit minors, can't we simply recycle some of the 
higher bits for additional partitions, across the board?  63 partitions 
seem to have been sufficient; at least I haven't heard anyone complain 
about that for 15 years.

	-hpa
-


From: Alan Cox <alan@...>
Subject: Re: [code] Unlimited partitions, a try
Date: Oct 5, 7:29 pm 2007

On Fri, 05 Oct 2007 15:11:52 -0700
"H. Peter Anvin" <hpa@zytor.com> wrote:

> Jan Engelhardt wrote:
> > 15 partitions (at least for sd_mod devices) are too few.
> 
> Now when we have 20-bit minors, can't we simply recycle some of the 
> higher bits for additional partitions, across the board?  63 partitions 
> seem to have been sufficient; at least I haven't heard anyone complain 
> about that for 15 years.

This was proposed ages ago. Al Viro vetoed sparse minors and it has been
stuck this way ever since. If you have > 15 partitions use device mapper
for it. I'd prefer it fixed but its arguable that device mapper is the
right way to punt all our partitioning to userspace


Alan
-


From: H. Peter Anvin <hpa@...>
Subject: Re: [code] Unlimited partitions, a try
Date: Oct 5, 7:29 pm 2007

Alan Cox wrote:
> On Fri, 05 Oct 2007 15:11:52 -0700
> "H. Peter Anvin" <hpa@zytor.com> wrote:
> 
>> Jan Engelhardt wrote:
>>> 15 partitions (at least for sd_mod devices) are too few.
>> Now when we have 20-bit minors, can't we simply recycle some of the 
>> higher bits for additional partitions, across the board?  63 partitions 
>> seem to have been sufficient; at least I haven't heard anyone complain 
>> about that for 15 years.
> 
> This was proposed ages ago. Al Viro vetoed sparse minors and it has been
> stuck this way ever since. If you have > 15 partitions use device mapper
> for it. I'd prefer it fixed but its arguable that device mapper is the
> right way to punt all our partitioning to userspace

Sure.  However, that takes having that bit of userspace in even the most 
trivial configurations, and not just on bootup, but continuously.

	-hpa
-


From: Bill Davidsen <davidsen@...>
Subject: Re: [code] Unlimited partitions, a try
Date: Oct 6, 3:33 pm 2007

H. Peter Anvin wrote:
> Alan Cox wrote:
>> On Fri, 05 Oct 2007 15:11:52 -0700
>> "H. Peter Anvin" <hpa@zytor.com> wrote:
>>
>>> Jan Engelhardt wrote:
>>>> 15 partitions (at least for sd_mod devices) are too few.
>>> Now when we have 20-bit minors, can't we simply recycle some of the 
>>> higher bits for additional partitions, across the board?  63 
>>> partitions seem to have been sufficient; at least I haven't heard 
>>> anyone complain about that for 15 years.
>>
>> This was proposed ages ago. Al Viro vetoed sparse minors and it has been
>> stuck this way ever since. If you have > 15 partitions use device mapper
>> for it. I'd prefer it fixed but its arguable that device mapper is the
>> right way to punt all our partitioning to userspace
> 
> Sure.  However, that takes having that bit of userspace in even the most 
> trivial configurations, and not just on bootup, but continuously.
> 
I'm not sure that configurations requiring more than 15 partitions are 
properly described as "trivial." Which is not to disagree with your 
point about required user tools, but most systems needing such tools 
will be large and complex enough that a userspace solution will be 
acceptable.


-- 
Bill Davidsen <davidsen@tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot
-