linux-kernel - Re: [CRIU] [PATCH 1/4] signalfd: add ability to return siginfo in a raw format

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Message-ID: <20121228144618.GC24229@redhat.com>
Date:	Fri, 28 Dec 2012 15:46:18 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrey Wagin <avagin@...il.com>
Cc:	Andrew Vagin <avagin@...allels.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	David Howells <dhowells@...hat.com>,
	linux-kernel@...r.kernel.org, criu@...nvz.org,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [CRIU] [PATCH 1/4] signalfd: add ability to return siginfo in
	a raw format

On 12/28, Andrey Wagin wrote:
>
> 2012/12/28 Oleg Nesterov <oleg@...hat.com>:
> >> >> @@ -321,6 +372,7 @@ SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
> >> >>               }
> >> >>
> >> >>               file->f_flags |= flags & SFD_RAW;
> >> >> +             file->f_mode |= FMODE_PREAD;
> >> >>
> >> >>               fd_install(ufd, file);
> >> >
> >> > Hmm. Looks like it is based on other patches I didnt see...
> >> >
> >> > But I don't understand how FMODE_PREAD connects to this patch, we need
> >> > this flag set even for regular sys_read() ???
> >>
> >> It doesn't need for sys_read(), but this patch is about pread() and
> >> sys_pread() checks it.
> >>
> >> SYSCALL_DEFINE(pread64)(unsigned int fd, char __user *buf,
> >>                         size_t count, loff_t pos)
> >> {
> >> ....
> >>         if (f.file) {
> >>                 ret = -ESPIPE;
> >>                 if (f.file->f_mode & FMODE_PREAD)
> >>                         ret = vfs_read(f.file, buf, count, &pos);
> >
> > And sys_read() checks it too, that was my point.
>
> sys_read() doesn't check this flag. I tryed to remove this code from
> this patch and pread returned ESPIPE as expected.

sys_read() calls vfs_read() which checks f_mode & FMODE_READ at the
start ?

Oleg.

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