From: Matthew Wilcox <matthew@wil.cx>
To: Kai Bankett <chaosman@ontika.net>
Cc: linux-fsdevel@vger.kernel.org
Subject: Re: QNX EFS Driver
Date: Fri, 23 Mar 2012 07:28:14 -0600 [thread overview]
Message-ID: <20120323132813.GJ19570@parisc-linux.org> (raw)
In-Reply-To: <4F6B6E63.8060200@ontika.net>
On Thu, Mar 22, 2012 at 07:24:35PM +0100, Kai Bankett wrote:
> Due to the fact that the QNX EFS Filesystem is not using any fixed
> blocks and just some fixed structures, I started fighting against the
> buffer head blocksize.
> I think I could pretty up the code a lot if there's any way to read N
> Bytes from a device at position X.
> Already started to look around, but could not really find something
> giving me direct position access to a device.
Sure; there's no need to use buffer_heads at all. You can call
submit_bio() to do reads and writes. You do have to be 512-byte aligned,
but that doesn't seem to be an issue for you. btrfs, ext4, gfs2, hfsplus,
jfs, logfs, nfs, nilfs2, ocfs2 and xfs all use the submit_bio interface
in case you need to see some examples.
> At least I would be extremly thankful if someone could point me some
> direction on how to better solve the chunkreading in qnxefs_file_read().
> It's currently buffer_head based with a blocksize of 512kb. The QNX EFS
> - at least the files I got hold of - uses 16384 byte Blocks in 262144
> byte logical units.
> So a file is split into chunks of up to 0x4000 size, but that chunks can
> vary in size. (in case of the end of a logical unit, file end etc.)
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
prev parent reply other threads:[~2012-03-23 13:28 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-22 18:24 QNX EFS Driver Kai Bankett
2012-03-23 13:28 ` Matthew Wilcox [this message]
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