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[RFC][PATCH v2] mmc_block: Allow more than 8 partitions per card

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  [RFC][PATCH v2] mmc_block: Allow more than 8 partitions per card John Stultz <john.stultz@linaro.org> - 2015-10-22 19:10 +0200
    Re: [RFC][PATCH v2] mmc_block: Allow more than 8 partitions per card Ben Hutchings <ben@decadent.org.uk> - 2015-10-22 20:10 +0200
      Re: [RFC][PATCH v2] mmc_block: Allow more than 8 partitions per card Ben Hutchings <ben@decadent.org.uk> - 2015-10-22 20:20 +0200

#1253983 — [RFC][PATCH v2] mmc_block: Allow more than 8 partitions per card

From: Colin Cross <ccross@android.com>

It is quite common for Android devices to utilize more
then 8 partitions on internal eMMC storage.

The vanilla kernel can support this via
CONFIG_MMC_BLOCK_MINORS, however that solution caps the
system to 256 minors total, which limits the number of
mmc cards the system can support.

This patch, which has been carried for quite awhile in
the AOSP common tree, provides an alternative solution
that doesn't seem to limit the total card count. So I
wanted to submit it for consideration upstream.

This patch sets the GENHD_FL_EXT_DEVT flag, which will
allocate minor number in major 259 for partitions past
disk->minors.

It also removes the use of disk_devt to determine devidx
from md->disk. md->disk->first_minor is always initialized
from devidx and can always be used to recover it.

Thoughts or feedback would be greatly appreciated.

Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Chuanxiao Dong <chuanxiao.dong@intel.com>
Cc: Shawn Lin <shawn.lin@rock-chips.com>
Cc: Austin S Hemmelgarn <ahferroin7@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Android Kernel Team <kernel-team@android.com>
Cc: linux-mmc@vger.kernel.org
Signed-off-by: Colin Cross <ccross@android.com>
[jstultz: Added context to commit message]
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
v2: Added context to commit message about CONFIG_MMC_BLOCK_MINORS
    and its limitations.

 drivers/mmc/card/block.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index c742cfd..564436e 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -172,11 +172,7 @@ static struct mmc_blk_data *mmc_blk_get(struct gendisk *disk)
 
 static inline int mmc_get_devidx(struct gendisk *disk)
 {
-	int devmaj = MAJOR(disk_devt(disk));
-	int devidx = MINOR(disk_devt(disk)) / perdev_minors;
-
-	if (!devmaj)
-		devidx = disk->first_minor / perdev_minors;
+	int devidx = disk->first_minor / perdev_minors;
 	return devidx;
 }
 
@@ -2162,6 +2158,7 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
 	md->disk->queue = md->queue.queue;
 	md->disk->driverfs_dev = parent;
 	set_disk_ro(md->disk, md->read_only || default_ro);
+	md->disk->flags = GENHD_FL_EXT_DEVT;
 	if (area_type & (MMC_BLK_DATA_AREA_RPMB | MMC_BLK_DATA_AREA_BOOT))
 		md->disk->flags |= GENHD_FL_NO_PART_SCAN;
 
-- 
1.9.1

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#1254020

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On Thu, 2015-10-22 at 10:00 -0700, John Stultz wrote:
> From: Colin Cross <ccross@android.com>
> 
> It is quite common for Android devices to utilize more
> then 8 partitions on internal eMMC storage.
> 
> The vanilla kernel can support this via
> CONFIG_MMC_BLOCK_MINORS, however that solution caps the
> system to 256 minors total, which limits the number of
> mmc cards the system can support.
[...]

This commit was intended to allow support for 256 cards with any number
of partitions:

commit a26eba614afff0e39594101bcb73014a9a22fb33
Author: Ben Hutchings <ben@decadent.org.uk>
Date:   Thu Nov 6 03:35:09 2014 +0000

    mmc: block: Increase max_devices

I don't think the new patch is sufficient or necessary to increase the
limit further.

Do you have a compatibility requirement to retain the numbering of the
first 7 partitions?

Ben.

-- 
Ben Hutchings
Q.  Which is the greater problem in the world today, ignorance or apathy?
A.  I don't know and I couldn't care less.

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#1254037

[Multipart message — attachments visible in raw view] — view raw

On Thu, 2015-10-22 at 19:07 +0100, Ben Hutchings wrote:
> On Thu, 2015-10-22 at 10:00 -0700, John Stultz wrote:
> > From: Colin Cross <ccross@android.com>
> > 
> > It is quite common for Android devices to utilize more
> > then 8 partitions on internal eMMC storage.
> > 
> > The vanilla kernel can support this via
> > CONFIG_MMC_BLOCK_MINORS, however that solution caps the
> > system to 256 minors total, which limits the number of
> > mmc cards the system can support.
> [...]
> 
> This commit was intended to allow support for 256 cards with any number
> of partitions:
> 
> commit a26eba614afff0e39594101bcb73014a9a22fb33
> Author: Ben Hutchings <ben@decadent.org.uk>
> Date:   Thu Nov 6 03:35:09 2014 +0000
> 
>     mmc: block: Increase max_devices
> 
> I don't think the new patch is sufficient or necessary to increase the
> limit further.

Of course, this does allow use of more than any predefined number of
partitions per card, the same as sd can.  So it still has some
usefulness, though the commit message seems to overstate that.

Ben.

> Do you have a compatibility requirement to retain the numbering of the
> first 7 partitions?
> 
> Ben.
> 
-- 
Ben Hutchings
Q.  Which is the greater problem in the world today, ignorance or apathy?
A.  I don't know and I couldn't care less.

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