linux-ext4 - Re: [RFC][PATCH 00/12] Enhanced file stat system call

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Message-Id: <E4DB425B-FE04-4A6A-806E-2BAFD0CB498E@dilger.ca>
Date:	Wed, 25 Nov 2015 12:30:33 -0700
From:	Andreas Dilger <adilger@...ger.ca>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	David Howells <dhowells@...hat.com>,
	Martin Steigerwald <martin@...htvoll.de>, arnd@...db.de,
	linux-afs@...r.kernel.org, linux-nfs@...r.kernel.org,
	linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-ext4@...r.kernel.org
Subject: Re: [RFC][PATCH 00/12] Enhanced file stat system call

On Nov 25, 2015, at 10:51 AM, J. Bruce Fields <bfields@...ldses.org> wrote:
> 
> On Fri, Nov 20, 2015 at 04:28:35PM +0000, David Howells wrote:
>> Martin Steigerwald <martin@...htvoll.de> wrote:
>> 
>>> Any plans to add limitations of filesystem to the call like maximum file
>>> size?  I know its mostly relevant for just for FAT32, but on any account
>>> rather than trying to write 4 GiB and then file, it would be good to at some
>>> time get a dialog at the beginning of the copy.
>> 
>> Adding filesystem limits can be done.  I got a shopping list of things people
>> wanted a while back and I've worked off of that list.  I can add other things
>> - that's on of the reasons I left room for expansion.
> 
> I ran across systemd/src/basic/path-util.c:fd_is_mount_point() the other
> day, and the contortions it goes through made me wonder if we should
> also add mnt_id and/or an is_mountpoint boolean--it's annoying to have
> to do name_to_handle_at() (not supported on all filesystems) just to get
> mnt_id.
> 
> (Looking at it now I see it falls back on reading mount id from
> /proc/self/fdinfo/<fd>.  Maybe that's good enough.  May depend on
> whether there's a potential user that doesn't want to assume access to
> /proc?)

IMHO, it should be possible to get information about a file or directory
from the file itself (i.e. statx() or fsinfo() on the path/fd), rather than
having to grub around in a /proc file that the application magically has to
know about, and parse text files there for every file being handled.

Cheers, Andreas






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