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Date: Wed, 8 Sep 2010 22:25:58 +0800
From: Lei Wen <adrian.wenl@...il.com>
To: Olof Johansson <olof@...om.net>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
Mandeep Baines <msb@...omium.org>
Subject: Re: [PATCH v3] mmc: add config and runtime option for number of
mmcblk minors
Hi,
On Sat, Aug 21, 2010 at 6:13 AM, Olof Johansson <olof@...om.net> wrote:
> The old limit of number of minor numbers per mmcblk device was hardcoded
> at 8. This isn't enough for some of the more elaborate partitioning
> schemes, for example those used by Chrome OS.
>
> Since there might be a bunch of systems out there with static /dev
> contents that relies on the old numbering scheme, let's make it a
> build-time option with the default set to the previous 8.
>
> Also provide a boot/modprobe-time parameter to override the config
> default: mmcblk.perdev_minors.
>
> Signed-off-by: Olof Johansson <olof@...om.net>
> Cc: Mandeep Baines <msb@...omium.org>
>
> ---
>
> Andrew, sorry for the churn but Mandeep had a couple of good points that
> needed addressing.
>
> Changes since v1:
> * Runtime override of config default
> * Better help text
> * DIV_ROUND_UP for max_devices calculation
> * Clarify mmcblk device count limitations
>
> Changes since v2 based on feedback from Mandeep Baines:
> * DIV_ROUND_UP is doing the wrong thing, we'll end up using
> the last fractional range of minors which we shouldn't.
> * Documentation/devices.txt update
> * No need to compute max_devices twice, just do it at runtime.
> * Permission fix for the module_param -- it's readonly.
>
> Documentation/devices.txt | 6 ++++++
> drivers/mmc/card/Kconfig | 17 +++++++++++++++++
> drivers/mmc/card/block.c | 41 ++++++++++++++++++++++++++++++-----------
> 3 files changed, 53 insertions(+), 11 deletions(-)
>
> diff --git a/Documentation/devices.txt b/Documentation/devices.txt
> index 1d83d12..fdf3821 100644
> --- a/Documentation/devices.txt
> +++ b/Documentation/devices.txt
> @@ -2518,6 +2518,12 @@ Your cooperation is appreciated.
> 8 = /dev/mmcblk1 Second SD/MMC card
> ...
>
> + The start of next SD/MMC card can be configured with
> + CONFIG_MMC_BLOCK_MINORS, or overridden at boot/modprobe
> + time using the mmcblk.perdev_minors option. That would
> + bump the offset between each card to be the configured
> + value instead of the default 8.
> +
> 179 char CCube DVXChip-based PCI products
> 0 = /dev/dvxirq0 First DVX device
> 1 = /dev/dvxirq1 Second DVX device
> diff --git a/drivers/mmc/card/Kconfig b/drivers/mmc/card/Kconfig
> index 3f2a912..57e4416 100644
> --- a/drivers/mmc/card/Kconfig
> +++ b/drivers/mmc/card/Kconfig
> @@ -14,6 +14,23 @@ config MMC_BLOCK
> mount the filesystem. Almost everyone wishing MMC support
> should say Y or M here.
>
> +config MMC_BLOCK_MINORS
> + int "Number of minors per block device"
> + range 4 256
> + default 8
> + help
> + Number of minors per block device. One is needed for every
> + partition on the disk (plus one for the whole disk).
> +
> + Number of total MMC minors available is 256, so your number
> + of supported block devices will be limited to 256 divided
> + by this number.
> +
> + Default is 8 to be backwards compatible with previous
> + hardwired device numbering.
> +
> + If unsure, say 8 here.
> +
> config MMC_BLOCK_BOUNCE
> bool "Use bounce buffer for simple hosts"
> depends on MMC_BLOCK
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index cb9fbc8..ec94f56 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -43,14 +43,26 @@
> #include "queue.h"
>
> MODULE_ALIAS("mmc:block");
> +#ifdef MODULE_PARAM_PREFIX
> +#undef MODULE_PARAM_PREFIX
> +#endif
> +#define MODULE_PARAM_PREFIX "mmcblk."
> +
> +
> +/*
> + * The defaults come from config options but can be overriden by module
> + * or bootarg options.
> + */
> +static int perdev_minors = CONFIG_MMC_BLOCK_MINORS;
>
> /*
> - * max 8 partitions per card
> + * We've only got one major, so number of mmcblk devices is
> + * limited to 256 / number of minors per device.
> */
> -#define MMC_SHIFT 3
> -#define MMC_NUM_MINORS (256 >> MMC_SHIFT)
> +static int max_devices;
>
> -static DECLARE_BITMAP(dev_use, MMC_NUM_MINORS);
> +/* 256 minors, so at most 256 separate devices */
> +static DECLARE_BITMAP(dev_use, 256);
>
> /*
> * There is one mmc_blk_data per slot.
> @@ -66,6 +78,9 @@ struct mmc_blk_data {
>
> static DEFINE_MUTEX(open_lock);
>
> +module_param(perdev_minors, int, 0444);
> +MODULE_PARM_DESC(perdev_minors, "Minors numbers to allocate per device");
> +
> static struct mmc_blk_data *mmc_blk_get(struct gendisk *disk)
> {
> struct mmc_blk_data *md;
> @@ -87,10 +102,10 @@ static void mmc_blk_put(struct mmc_blk_data *md)
> md->usage--;
> if (md->usage == 0) {
> int devmaj = MAJOR(disk_devt(md->disk));
> - int devidx = MINOR(disk_devt(md->disk)) >> MMC_SHIFT;
> + int devidx = MINOR(disk_devt(md->disk)) / perdev_minors;
>
> if (!devmaj)
> - devidx = md->disk->first_minor >> MMC_SHIFT;
> + devidx = md->disk->first_minor / perdev_minors;
>
> blk_cleanup_queue(md->queue.queue);
>
> @@ -482,8 +497,8 @@ static struct mmc_blk_data *mmc_blk_alloc(struct mmc_card *card)
> struct mmc_blk_data *md;
> int devidx, ret;
>
> - devidx = find_first_zero_bit(dev_use, MMC_NUM_MINORS);
> - if (devidx >= MMC_NUM_MINORS)
> + devidx = find_first_zero_bit(dev_use, max_devices);
> + if (devidx >= max_devices)
> return ERR_PTR(-ENOSPC);
> __set_bit(devidx, dev_use);
>
> @@ -500,7 +515,7 @@ static struct mmc_blk_data *mmc_blk_alloc(struct mmc_card *card)
> */
> md->read_only = mmc_blk_readonly(card);
>
> - md->disk = alloc_disk(1 << MMC_SHIFT);
> + md->disk = alloc_disk(perdev_minors);
> if (md->disk == NULL) {
> ret = -ENOMEM;
> goto err_kfree;
> @@ -517,7 +532,7 @@ static struct mmc_blk_data *mmc_blk_alloc(struct mmc_card *card)
> md->queue.data = md;
>
> md->disk->major = MMC_BLOCK_MAJOR;
> - md->disk->first_minor = devidx << MMC_SHIFT;
> + md->disk->first_minor = devidx * perdev_minors;
> md->disk->fops = &mmc_bdops;
> md->disk->private_data = md;
> md->disk->queue = md->queue.queue;
> @@ -593,7 +608,6 @@ static int mmc_blk_probe(struct mmc_card *card)
> {
> struct mmc_blk_data *md;
> int err;
> -
> char cap_str[10];
>
> /*
> @@ -683,6 +697,11 @@ static int __init mmc_blk_init(void)
> {
> int res;
>
> + if (perdev_minors != CONFIG_MMC_BLOCK_MINORS)
> + pr_info("mmcblk: using %d minors per device\n", perdev_minors);
> +
> + max_devices = 256 / perdev_minors;
> +
> res = register_blkdev(MMC_BLOCK_MAJOR, "mmc");
> if (res)
> goto out;
> --
> 1.5.6.5
>
The patch's purpose is good. As modern sd&mmc is used to host the file
system, the 8 partition limitation is becoming a kind of bottleneck...
But why not just add GENHD_FL_EXT_DEVT flag to allow mmc use extended
partition numbers?
Like this modification?
diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index 8d2bd24..2e3eeb1 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -557,6 +557,7 @@ static struct mmc_blk_data *mmc_blk_alloc(struct
mmc_card *card)
md->disk->private_data = md;
md->disk->queue = md->queue.queue;
md->disk->driverfs_dev = &card->dev;
+ md->disk->flags |= GENHD_FL_EXT_DEVT;
/*
* As discussed on lkml, GENHD_FL_REMOVABLE should:
Best regards,
Lei
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