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Date:   Thu, 19 Mar 2020 07:33:10 -0300
From:   Bruno Meneguele <bmeneg@redhat.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        pmladek@suse.com, sergey.senozhatsky@gmail.com, rostedt@goodmis.org
Subject: Re: [PATCH] kernel/printk: add kmsg SEEK_CUR handling
Message-ID: <20200319103310.GE3448@glitch>
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 <20200313110229.GI13406@glitch>
 <20200317020326.GC219881@google.com>
 <20200317085358.GE11152@glitch>
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On Tue, Mar 17, 2020 at 05:54:00AM -0300, Bruno Meneguele wrote:
> On Tue, Mar 17, 2020 at 11:03:26AM +0900, Sergey Senozhatsky wrote:
> > On (20/03/13 08:02), Bruno Meneguele wrote:
> > > Ok, I poorly expressed the notion of "documentantion". The userspace
> > > doesn't tell about returning -ESPIPE, but to the functions work prope=
rly
> > > they watch for -ESPIPE returning from the syscall. For instance, gbli=
c
> > > dprintf() implementation:
> > >=20
> > > dprintf:
> > >   __vdprintf_internal:
> > >     _IO_new_file_attach:
> > >=20
> > >   if (_IO_SEEKOFF (fp, (off64_t)0, _IO_seek_cur, _IOS_INPUT|_IOS_OUTP=
UT)
> > >       =3D=3D _IO_pos_BAD && errno !=3D ESPIPE)
> > >     return NULL;
> > >=20
> > > With that, if the seek fails, but return anything other than ESPIPE t=
he
> > > dprintf() will also fail returning -EINVAL to dprintf() caller. While=
 if
> > > ESPIPE is returned, it's "ignored" and the call still works. The way =
we
> > > have today make kmsg an exception case among the rest of the system
> > > files where you can open with dprintf.
> > >=20
> > > One of the things I could agree with is removing the SEEK call from
> > > dprintf, since fprintf basically follows the same steps, but doesn't
> > > seek anything.  But at the same time, IMO it makes sense to make kmsg
> > > interface complaint with the errno return values.
> >=20
> > The code in questions is very old. So let's add the missing bit to the
> > kernel. At the same time, we probably can have a slightly more detailed
> > documentation / code comment.
> >=20
> > =09-ss
> >=20
>=20
> Sure thing.
>=20
> I'm going to send a v2 of this patch with more details still today or
> tomorrow.
>=20
> Thanks!
>=20

Just fyi, v2 was posted:
https://lkml.org/lkml/2020/3/17/321

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