Re: [RFC PATCH v2 1/9] block: add nr_mirrors to request_queue

[Andreas Dilger <adilger@dilger.ca>]

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On Feb 13, 2019, at 2:50 AM, Bob Liu <bob.liu@oracle.com> wrote:
> 
> When fs data/metadata checksum mismatch, lower block devices may have other
> correct copies. e.g if we did raid1 for protecting fs metadata.
> Then fs could try other copies of metadata instead of panic, but fs need be
> awared how many mirrors the block devices have.
> 
> This patch add @nr_mirrors to struct request_queue which is similar as
> blk_queue_nonrot(), filesystem can grab device request queue and check the
> number of mirrors of this block device.
> 
> @nr_mirrors is 1 by default which means only one copy, drivers e.g raid1 are
> responsible for setting the right value. The maximum value is
> BITS_PER_LONG which is 32 or 64. That should be big enough else retry lantency
> may be too high.
> 
> Also added helper functions for get/set the number of mirrors for a specific
> device request queue.
> 
> Todo:
> * Export nr_mirrors through /sysfs.
> 
> Signed-off-by: Bob Liu <bob.liu@oracle.com>

> diff --git a/block/blk-settings.c b/block/blk-settings.c
> index 3e7038e475ee..38e4d7e675e6 100644
> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> @@ -844,6 +844,30 @@ void blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)
> +/*
> + * Set the number of read redundant mirrors.
> + */
> +bool blk_queue_set_mirrors(struct request_queue *q, unsigned short mirrors)
> +{
> +	if(q->nr_mirrors >= BLKDEV_MAX_MIRRORS) {
> +		printk("blk_queue_set_mirrors: %d exceed max mirrors(%d)\n",
> +				mirrors, BLKDEV_MAX_MIRRORS);

Need to supply a KERN_ level here.

Cheers, Andreas






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