linux-kernel - Re: For review: open_by_name

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Message-ID: <53283DFB.6040105@gmail.com>
Date:	Tue, 18 Mar 2014 13:37:15 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Christoph Hellwig <hch@...radead.org>, NeilBrown <neilb@...e.de>
CC:	mtk.manpages@...il.com,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Andreas Dilger <adilger@...ger.ca>
Subject: Re: For review: open_by_name_at(2) man page

On 03/18/2014 10:43 AM, Christoph Hellwig wrote:
> On Tue, Mar 18, 2014 at 09:00:07AM +1100, NeilBrown wrote:
>> ESTALE is also returned if the filesystem does not support file-handle ->
>> file mappings.
>> On filesystems which don't provide export_operations (/sys /proc ubifs
>> romfs cramfs nfs coda ... several others) name_to_handle_at will produce a
>> generic handle using the 32 bit inode and 32 bit i_generation.
> 
> Do we?  Seems like the code is erroring out early if there are no
> export_ops?

It appears to me that Neil's statement isn't correct, at least for /proc
and /sys (see my other mail, to Neil). I'm unsure about whether it is true
for some of those other FSes thought.

>> Does it?  My understanding from "man libblkid" (it is a while since I've read
>> the code) is that it either uses info in /dev/disks/by-* or reads directly
>> from the block devices (maybe using /sys to find them?) and interprets the
>> superblock to extract a UUID.
> 
> It normally reads directly from disk, unless it has changed very
> recently.

Thanks. As noted in my mail, I solved this one by just saying a little less
about libblkid.

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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