linux-ext4 - Re: [RFC PATCH 1/2] bdi: Create a flag to indicate that a backing device needs stable page writes

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Date:	Mon, 29 Oct 2012 19:13:58 +0100
From:	Jan Kara <jack@...e.cz>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	Theodore Ts'o <tytso@....edu>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [RFC PATCH 1/2] bdi: Create a flag to indicate that a backing
 device needs stable page writes

On Fri 26-10-12 18:35:24, Darrick J. Wong wrote:
> This creates BDI_CAP_STABLE_WRITES, which indicates that a device requires
> stable page writes.  It also plumbs in a sysfs attribute so that admins can
> check the device status.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
  I guess Jens Axboe <axboe@...nel.dk> would be the best target for this
patch (so that he can merge it). The patch looks OK to me. You can add:
  Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
> 
>  block/blk-integrity.c       |    8 ++++++++
>  include/linux/backing-dev.h |    6 ++++++
>  mm/backing-dev.c            |   11 +++++++++++
>  3 files changed, 25 insertions(+)
> 
> diff --git a/block/blk-integrity.c b/block/blk-integrity.c
> index da2a818..d05d7b3 100644
> --- a/block/blk-integrity.c
> +++ b/block/blk-integrity.c
> @@ -384,6 +384,7 @@ EXPORT_SYMBOL(blk_integrity_is_initialized);
>  int blk_integrity_register(struct gendisk *disk, struct blk_integrity *template)
>  {
>  	struct blk_integrity *bi;
> +	struct backing_dev_info *bdi;
>  
>  	BUG_ON(disk == NULL);
>  
> @@ -420,6 +421,9 @@ int blk_integrity_register(struct gendisk *disk, struct blk_integrity *template)
>  	} else
>  		bi->name = bi_unsupported_name;
>  
> +	bdi = &disk->queue->backing_dev_info;
> +	bdi->capabilities |= BDI_CAP_STABLE_WRITES;
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL(blk_integrity_register);
> @@ -434,10 +438,14 @@ EXPORT_SYMBOL(blk_integrity_register);
>  void blk_integrity_unregister(struct gendisk *disk)
>  {
>  	struct blk_integrity *bi;
> +	struct backing_dev_info *bdi;
>  
>  	if (!disk || !disk->integrity)
>  		return;
>  
> +	bdi = &disk->queue->backing_dev_info;
> +	bdi->capabilities &= ~BDI_CAP_STABLE_WRITES;
> +
>  	bi = disk->integrity;
>  
>  	kobject_uevent(&bi->kobj, KOBJ_REMOVE);
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 2a9a9ab..b82a8bb 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -253,6 +253,7 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
>  #define BDI_CAP_EXEC_MAP	0x00000040
>  #define BDI_CAP_NO_ACCT_WB	0x00000080
>  #define BDI_CAP_SWAP_BACKED	0x00000100
> +#define BDI_CAP_STABLE_WRITES	0x00000200
>  
>  #define BDI_CAP_VMFLAGS \
>  	(BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP)
> @@ -307,6 +308,11 @@ long wait_iff_congested(struct zone *zone, int sync, long timeout);
>  int pdflush_proc_obsolete(struct ctl_table *table, int write,
>  		void __user *buffer, size_t *lenp, loff_t *ppos);
>  
> +static inline bool bdi_cap_stable_writes(struct backing_dev_info *bdi)
> +{
> +	return bdi->capabilities & BDI_CAP_STABLE_WRITES;
> +}
> +
>  static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi)
>  {
>  	return !(bdi->capabilities & BDI_CAP_NO_WRITEBACK);
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index d3ca2b3..a2f4c08 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -221,12 +221,23 @@ static ssize_t max_ratio_store(struct device *dev,
>  }
>  BDI_SHOW(max_ratio, bdi->max_ratio)
>  
> +static ssize_t stable_page_writes_show(struct device *dev,
> +	struct device_attribute *attr, char *page)
> +{
> +	struct backing_dev_info *bdi = dev_get_drvdata(dev);
> +
> +	return snprintf(page, PAGE_SIZE-1, "%d\n",
> +			bdi->capabilities & BDI_CAP_STABLE_WRITES ? 1 : 0);
> +}
> +
>  #define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
> +#define __ATTR_RO(attr) __ATTR(attr, 0444, attr##_show, NULL)
>  
>  static struct device_attribute bdi_dev_attrs[] = {
>  	__ATTR_RW(read_ahead_kb),
>  	__ATTR_RW(min_ratio),
>  	__ATTR_RW(max_ratio),
> +	__ATTR_RO(stable_page_writes),
>  	__ATTR_NULL,
>  };
>  
> --
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-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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