linux-ext4 - RE: Is it possible for the ext4/btrfs file system to pass some context related info to low level block driver?

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Date:	Wed, 4 May 2011 18:31:19 +0800
From:	"Gao, Yunpeng" <yunpeng.gao@...el.com>
To:	Kyungmin Park <kmpark@...radead.org>
CC:	"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>
Subject: RE: Is it possible for the ext4/btrfs file system to pass some
 context related info to low level block driver?

Hi Park,

Thanks a lot for the response.

>It seems similar with TRIM. So how about to consider TRIM
>implementation or extend it?

Yes, file system set REQ_DISCARD flag to notify block device driver to execute TRIM.
And I noticed there's already a flag REQ_META used for file system meta data.
But seems only gfs2 file system uses the REQ_META flag, other file systems (including ext4 and btrfs) have not used this flag.
Is the flag useless or any other reason?

>I'm not familiar with NCQ implementation but it's also helpful to implement it.

I don't know much about NCQ, too. Just have a impression that NCQ is only for SATA hard disk, can it also be used for block device, such as the mmc block device?

Thanks.

Regards,
Yunpeng

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