Re: [PATCH 1/4] gpio: userspace ABI for reading/writing GPIO lines

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Wed, Jun 29, 2016 at 10:53 AM, Alexander Stein
<alexander.stein@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Thursday 02 June 2016 13:51:26, Linus Walleij wrote:

>> +     fd = anon_inode_getfd("gpio-linehandle",
>> +                           &linehandle_fileops,
>> +                           lh,
>> +                           O_RDONLY | O_CLOEXEC);
>
> When will linehandle_release actually be called? When we explicitely call
> close(req.fd) or when application exits and all FDs will be closed anyway?

As far as I understand: both.

And I don't think anything else makes sense? If an application is terminated,
the operating environment will close all open file handles as far as I know,
at least that is how I always thought it works.

But hey, it's userspace so what do I know...

Anyways if it doesn't work like so, there are a bunch of subsystems in
the kernel using it so they would all have severe problems.

>> +     if (fd < 0) {
>> +             ret = fd;
>> +             goto out_free_descs;
>> +     }
>> +
>> +     handlereq.fd = fd;
>> +     if (copy_to_user(ip, &handlereq, sizeof(handlereq)))
>> +             return -EFAULT;
>
> If I'm right above doesn't that then leak lh until application eventually
> exits? Userspace won't receive the newly created fd. The same would apply to
> patch 3/4.

I don't understand....

The userspace application reads the .fd fields of the handle request after
issuing the ioctl() and it then contains the new file handle.

Yours,
Linus Walleij
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