linux-kernel - Re: [PATCH 0/8] introduce dynamic device creation/removal

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Date:	Fri, 27 Feb 2015 14:51:09 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Minchan Kim <minchan@...nel.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH 0/8] introduce dynamic device creation/removal

On Thu, 26 Feb 2015 23:10:35 +0900 Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:

> Hello,
> 
> this patchset introduces dynamic (on demand) zram device add-remove
> functionality via /dev/zram-control interface. Two ioctl commands are
> defined as of now (accessible in user-space via new zram.h header file):
> -- ZRAM_CTL_ADD
> 	add new device (generates device_id automatically or uses provided
> 	device_id)
> -- ZRAM_CTL_REMOVE
> 	remove device (by device_id)
> 
> util-linux zramctl update will be done later, after we land this patchset.
> 
> 
> This also opens a possibility to drop some of sysfs device attrs and FOO_show()
> code duplication in the future, and provide device stats/info via ioctl call
> instead, providing something like (via zram.h):
> 
> 	struct zram_info {
> 		__u64 orig_data_size;
> 		__u64 mem_used_total;
> 		__u64 max_comp_streams;
> 
> 		[..]
> 	};
> 
> 
> fill it under ->init_lock in zram_fill_info() (or any other name) function and
> return all device stats at once back to user-space in a single syscall.
> 
> This is a long term plan, of course, but I'd like to see sysfs functions go away
> in a year or so. What do you think?

hoo boy.  Creating a /dev node and doing ioctls on it is really old
school.  So old school that I've forgotten why we don't do it any more.

Hopefully Alan can recall the thinking?
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