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From: "Theodore Ts'o" <tytso@mit.edu>
To: David Howells <dhowells@redhat.com>
Cc: viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, xfs@oss.sgi.com
Subject: Re: [RFC PATCH 1/2] VFS: Kill use of O_LARGEFILE inside the kernel
Date: Tue, 22 Sep 2015 15:25:27 -0400	[thread overview]
Message-ID: <20150922192527.GA3318@thunk.org> (raw)
In-Reply-To: <1458.1442938362@warthog.procyon.org.uk>

On Tue, Sep 22, 2015 at 05:12:42PM +0100, David Howells wrote:
> 
> Further, path-based truncate() makes no checks based on file-largeness, unlike
> ftruncate().

Right, but truncate in general is used to make files *smaller* so I'm
having trouble thinking of a scenario where a largefile-oblivious
program could get in trouble by truncating a file > 2TB to some
hard-coded length (normally zero).

> Overlayfs and one or two other places need to potentially apply O_LARGEFILE to
> the things that they do on behalf of userspace - but other than suppressing
> some size checks, it seems to be ignored by the filesystems and the VM.

The size checks really were the primary points of O_LARGEFILE.  As I
recall the primary system calls where this really matters is open(2)
and stat(2) (since if st_size is too small to represent the size of
the file, then the user space program could get really confused).

Essentially O_LARGEFILE is an assertion that userspace can handle
handle 64-bit files, and won't get confused by system call interfaces
where off_t is 32-bit wide, because it will use the 64-bit variants.
So it's not at all surprising that the file systems and the VM in
general doesn't need to worry about the flag.

    	       	   	      	      - Ted

WARNING: multiple messages have this Message-ID (diff)
From: Theodore Ts'o <tytso@mit.edu>
To: David Howells <dhowells@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, xfs@oss.sgi.com,
	viro@zeniv.linux.org.uk, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/2] VFS: Kill use of O_LARGEFILE inside the kernel
Date: Tue, 22 Sep 2015 15:25:27 -0400	[thread overview]
Message-ID: <20150922192527.GA3318@thunk.org> (raw)
In-Reply-To: <1458.1442938362@warthog.procyon.org.uk>

On Tue, Sep 22, 2015 at 05:12:42PM +0100, David Howells wrote:
> 
> Further, path-based truncate() makes no checks based on file-largeness, unlike
> ftruncate().

Right, but truncate in general is used to make files *smaller* so I'm
having trouble thinking of a scenario where a largefile-oblivious
program could get in trouble by truncating a file > 2TB to some
hard-coded length (normally zero).

> Overlayfs and one or two other places need to potentially apply O_LARGEFILE to
> the things that they do on behalf of userspace - but other than suppressing
> some size checks, it seems to be ignored by the filesystems and the VM.

The size checks really were the primary points of O_LARGEFILE.  As I
recall the primary system calls where this really matters is open(2)
and stat(2) (since if st_size is too small to represent the size of
the file, then the user space program could get really confused).

Essentially O_LARGEFILE is an assertion that userspace can handle
handle 64-bit files, and won't get confused by system call interfaces
where off_t is 32-bit wide, because it will use the 64-bit variants.
So it's not at all surprising that the file systems and the VM in
general doesn't need to worry about the flag.

    	       	   	      	      - Ted

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  reply	other threads:[~2015-09-22 19:25 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-22 15:24 [RFC PATCH 1/2] VFS: Kill use of O_LARGEFILE inside the kernel David Howells
2015-09-22 15:24 ` David Howells
2015-09-22 15:25 ` [RFC PATCH 2/2] VFS: Don't pass O_LARGEFILE when opening a file internally David Howells
2015-09-22 15:25   ` David Howells
2015-09-22 15:51 ` [RFC PATCH 1/2] VFS: Kill use of O_LARGEFILE inside the kernel Theodore Ts'o
2015-09-22 15:51   ` Theodore Ts'o
2015-09-22 16:12 ` David Howells
2015-09-22 16:12   ` David Howells
2015-09-22 19:25   ` Theodore Ts'o [this message]
2015-09-22 19:25     ` Theodore Ts'o
2015-09-22 21:45   ` Dave Chinner
2015-09-22 21:45     ` Dave Chinner

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