linux-kernel - Re: [PATCH] agp: remove read/write stubs

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Message-ID: <CA+rthh_L1_9FoSg7HsjSjVkG_HQNCWLgzp3q1-jBrxt_FMOpdw@mail.gmail.com>
Date:	Tue, 22 Jul 2014 21:50:01 +0200
From:	Mathias Krause <minipli@...glemail.com>
To:	Dave Airlie <airlied@...il.com>
Cc:	David Airlie <airlied@...ux.ie>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] agp: remove read/write stubs

On 9 July 2014 08:52, Mathias Krause <minipli@...glemail.com> wrote:
> On 9 July 2014 00:48, Dave Airlie <airlied@...il.com> wrote:
>> On 2 July 2014 16:15, Mathias Krause <minipli@...glemail.com> wrote:
>>> On 15 June 2014 23:02, Mathias Krause <minipli@...glemail.com> wrote:
>>>> The VFS layer handles those in the very same way, if unset. No need for
>>>> additional stubs.
>>>>
>>>> Signed-off-by: Mathias Krause <minipli@...glemail.com>
>>>> Cc: Alexander Viro <viro@...iv.linux.org.uk>
>>>> ---
>>>>  drivers/char/agp/frontend.c |   15 ---------------
>>>>  1 file changed, 15 deletions(-)
>>>>
>>>> diff --git a/drivers/char/agp/frontend.c b/drivers/char/agp/frontend.c
>>>> index b29703324e..09f17eb734 100644
>>>> --- a/drivers/char/agp/frontend.c
>>>> +++ b/drivers/char/agp/frontend.c
>>>> @@ -710,19 +710,6 @@ static int agp_open(struct inode *inode, struct file *file)
>>>>         return 0;
>>>>  }
>>>>
>>>> -
>>>> -static ssize_t agp_read(struct file *file, char __user *buf,
>>>> -                       size_t count, loff_t * ppos)
>>>> -{
>>>> -       return -EINVAL;
>>>> -}
>>>> -
>>>> -static ssize_t agp_write(struct file *file, const char __user *buf,
>>>> -                        size_t count, loff_t * ppos)
>>>> -{
>>>> -       return -EINVAL;
>>>> -}
>>>> -
>>>>  static int agpioc_info_wrap(struct agp_file_private *priv, void __user *arg)
>>>>  {
>>>>         struct agp_info userinfo;
>>>> @@ -1047,8 +1034,6 @@ static const struct file_operations agp_fops =
>>>>  {
>>>>         .owner          = THIS_MODULE,
>>>>         .llseek         = no_llseek,
>>>> -       .read           = agp_read,
>>>> -       .write          = agp_write,
>>>>         .unlocked_ioctl = agp_ioctl,
>>>>  #ifdef CONFIG_COMPAT
>>>>         .compat_ioctl   = compat_agp_ioctl,
>>>> --
>>>> 1.7.10.4
>>>>
>>>
>>> Ping. Any objections, comments? David?
>>
>> Are you sure VFS handles this the same way? can you point me where it
>> checks ->read and returns -EINVAL, I'm probably just missing it in my
>> quick look over fs/read_write.c
>
> The VFS code changed during the last merge window so the ->read and
> ->write tests are no longer directly visible. The presence of a ->read
> / ->write function is now remembered at open(2) time and stored in
> ->f_mode as a flag.
>
> The corresponding commit for the VFS change is 7f7f25e82d "replace
> checking for ->read/->aio_read presence with check in ->f_mode".
> Despite its subject, it also handles ->write / ->aio_write. The flags
> are set in fs/open:do_dentry_open():
>
>     if ((f->f_mode & FMODE_READ) &&
>          likely(f->f_op->read || f->f_op->aio_read || f->f_op->read_iter))
>         f->f_mode |= FMODE_CAN_READ;
>     if ((f->f_mode & FMODE_WRITE) &&
>          likely(f->f_op->write || f->f_op->aio_write || f->f_op->write_iter))
>         f->f_mode |= FMODE_CAN_WRITE;
>
> With that change in mind, the redundancy of the agp_read() and
> agp_write() functions can be seen for read(2) in vfs_read():
>
>     if (!(file->f_mode & FMODE_CAN_READ))
>         return -EINVAL;
>
> ..and for write(2) in vfs_write():
>
>     if (!(file->f_mode & FMODE_CAN_WRITE))
>         return -EINVAL;
>
> The other entry points (readv / writev / compat wrappers) have been
> changed accordingly, so those handle a missing ->read / ->write
> callback in the same way: returning -EINVAL.
>
> Regards,
> Mathias

Ping. Any more comments, David?
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