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Date: Wed, 4 Mar 2015 17:36:07 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nitin Gupta <ngupta@vflare.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/8] zram: add dynamic device add/remove functionality
Message-ID: <20150304083607.GE574@swordfish>
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On (03/04/15 17:19), Sergey Senozhatsky wrote:
> hm... that actually doesn't look so hard.
> 
> all I need to do is just change zram_add attr to RW (or create a new RO
> attribute `zram_auto_add', or whatever) and treat read access to that
> zram_add_read() or zram_auto_add_read() attr as (atomic operation):
> 	-- generate new device_id X
> 	-- create corresponding zramX device
> 	-- return that X as char *text to user space (or error). the
> 	same way we sprintf() stats.
> 
> what do you think? I'll play with it.
> 

that will do the trick. testing simple patch:

# cat /sys/class/zram-control/zram_add
1
# cat /sys/class/zram-control/zram_add
2
# cat /sys/class/zram-control/zram_add
3
# cat /sys/class/zram-control/zram_add
4
# cat /sys/class/zram-control/zram_add
5

dmesg:
[14339.063075] zram: Added device: zram1
[14339.972633] zram: Added device: zram2
[14340.626564] zram: Added device: zram3
[14341.242134] zram: Added device: zram4
[14341.850853] zram: Added device: zram5


try to add already existing device_id

# echo 3 > /sys/class/zram-control/zram_add
-bash: echo: write error: File exists


zram_add() error propogation to user space (-ENOMEM in this case)

# cat /sys/class/zram-control/zram_add
cat: /sys/class/zram-control/zram_add: Cannot allocate memory


will send out new patch set later today.

	-ss