Re: [PATCH 2/5] block: add function to issue compare and write

Re: [PATCH 2/5] block: add function to issue compare and write

[Christoph Hellwig]

On Thu, Oct 16, 2014 at 12:37:12AM -0500, michaelc@cs.wisc.edu wrote:
> @@ -160,7 +160,7 @@ enum rq_flag_bits {
>  	__REQ_DISCARD,		/* request to discard sectors */
>  	__REQ_SECURE,		/* secure discard (used with __REQ_DISCARD) */
>  	__REQ_WRITE_SAME,	/* write same block many times */
> -
> +	__REQ_CMP_AND_WRITE,	/* compare data and write if matched */

I think it's time that we stop overloading the request flags with
request types.

We already have req->cmd_type which actually is a fairly good
description of what we get except for REQ_TYPE_FS, which is a horrible
overload using req->cmd_flags.

Given that you're just one of many currently ongoing patches to add
more flags here I think you need to byte the bullet and fix this up
by replacing REQ_TYPE_FS with:

REQ_TYPE_WRITE
REQ_TYPE_READ
REQ_TYPE_FLUSH
REQ_TYPE_DISCARD
REQ_TYPE_WRITE_SAME
REQ_TYPE_CMP_AND_WRITE

sd.c is a nice guide of what should be a flag and what a type since my
last refactoring of the command_init function.

Re: [PATCH 2/5] block: add function to issue compare and write

[Martin K. Petersen]

>>>>> "Christoph" == Christoph Hellwig <hch@infradead.org> writes:

Christoph> We already have req->cmd_type which actually is a fairly good
Christoph> description of what we get except for REQ_TYPE_FS, which is a
Christoph> horrible overload using req->cmd_flags.

Christoph> Given that you're just one of many currently ongoing patches
Christoph> to add more flags here I think you need to byte the bullet
Christoph> and fix this up by replacing REQ_TYPE_FS with:

Christoph> REQ_TYPE_WRITE REQ_TYPE_READ REQ_TYPE_FLUSH REQ_TYPE_DISCARD
Christoph> REQ_TYPE_WRITE_SAME REQ_TYPE_CMP_AND_WRITE

The problem with this is that, as it stands, a bio has no type. And it
would suck if we couldn't keep bio rw and request flags in sync.

I wonder if it would make more sense to move the remaining rq types to
cmd_flags after I'm done with the 64-bit conversion?

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: [PATCH 2/5] block: add function to issue compare and write

[Christoph Hellwig]

On Fri, Oct 17, 2014 at 07:38:37PM -0400, Martin K. Petersen wrote:
> The problem with this is that, as it stands, a bio has no type. And it
> would suck if we couldn't keep bio rw and request flags in sync.
> 
> I wonder if it would make more sense to move the remaining rq types to
> cmd_flags after I'm done with the 64-bit conversion?

I'd prefer adding a cmd_type to the bio as well and avoid the 64-bit
flag conversion.  While we'll probably grow more types of I/Os (e.g.
copy offload) I hope we can actually reduce the number of real flags,
and it's easier to read for sure if we can switch on the command type
in the driver.