From: Tejun Heo <tj@kernel.org>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>,
Kay Sievers <kay@vrfy.org>,
linux-next@vger.kernel.org
Subject: Re: [BUG -next] sysfs change breaks userspace
Date: Fri, 1 Nov 2013 11:08:00 -0400 [thread overview]
Message-ID: <20131101150800.GE20005@htj.dyndns.org> (raw)
In-Reply-To: <20131101150448.GB18600@kroah.com>
Hello, Greg.
On Fri, Nov 01, 2013 at 08:04:48AM -0700, Greg Kroah-Hartman wrote:
> > @@ -800,7 +800,7 @@ EXPORT_SYMBOL_GPL(sysfs_notify);
> > const struct file_operations sysfs_file_operations = {
> > .read = seq_read,
> > .write = sysfs_write_file,
> > - .llseek = seq_lseek,
> > + .llseek = generic_file_llseek,
>
> Does that mean that seq_lseek can't handle SEEK_END? Shouldn't we fix
> that instead?
As the files are dynamic, seq_file has no way of knowing whether the
file is gonna end at all. It's perfectly valid to have an infinite
file. The only benefits of using seq_lseek() instead of
generic_file_llseek() are
* Early failure. For whatever reason, traversing to certain file
position should fail, seq_lseek() will report such failure on
seek(2) instead of the following read/write operations.
* EOF detection. While SEEK_END is not supported, SEEK_SET/CUR +
large offset can be used to detect eof - eof at the time of the last
seek anyway as the file size may change dynamically.
I don't think either would matter for sysfs or for prospect kernfs
users and sticking with genefic_file_llseek() should be fine.
Thanks.
--
tejun
next prev parent reply other threads:[~2013-11-01 15:08 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-31 11:43 [BUG -next] sysfs change breaks userspace Heiko Carstens
2013-10-31 17:25 ` Tejun Heo
2013-11-01 14:13 ` Heiko Carstens
2013-11-01 14:35 ` Tejun Heo
2013-11-01 15:04 ` Greg Kroah-Hartman
2013-11-01 15:08 ` Tejun Heo [this message]
2013-11-01 16:14 ` Greg Kroah-Hartman
2013-11-01 17:16 ` [PATCH driver-core-next] sysfs: use generic_file_llseek() for sysfs_file_operations Tejun Heo
2013-11-01 17:19 ` Greg Kroah-Hartman
2013-11-01 18:40 ` Heiko Carstens
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