linux-kernel - Re: PROBLEM: Firmware loader fallback mechanism no longer works with sendfile

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Message-ID: <180bdfaf-8c84-6946-b46f-3729d4eb17cc@codeaurora.org>
Date:   Tue, 5 Jan 2021 17:00:58 -0800
From:   Siddharth Gupta <sidgup@...eaurora.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     mcgrof@...nel.org, rafael@...nel.org, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "psodagud@...eaurora.org" <psodagud@...eaurora.org>
Subject: Re: PROBLEM: Firmware loader fallback mechanism no longer works with
 sendfile


On 1/4/2021 10:36 PM, Greg KH wrote:
> On Mon, Jan 04, 2021 at 02:43:45PM -0800, Siddharth Gupta wrote:
>> Hi all,
>>
>> With the introduction of the filesystem change "fs: don't allow splice
>> read/write without explicit ops"[1] the fallback mechanism of the firmware
>> loader[2] no longer works when using sendfile[3] from the userspace.
> What userspace program are you using to load firmware?
The userspace program is in the android userspace which listens to a 
uevent from the firmware loader and then loads the firmware using 
sendfile[1].
>   Are you not using the in-kernel firmware loader for some reason?
We have certain non-standard firmware paths that should not be added to 
the linux kernel, and the firmware_class.path only supports a single path.
>
>> Since the binary attributes don't support splice_{read,write} functions the
>> calls to splice_{read,write} used the default kernel_{read,write} functions.
>> With the above change this results in an -EINVAL return from
>> do_splice_from[4].
>>
>> This essentially means that sendfile will not work for any binary attribute
>> in the sysfs.
> Have you tried fixing this with a patch much like what we did for the
> proc files that needed this?  If not, can you?
I am not aware of this fix, could you provide me a link for reference? I 
will try it out.
>
>> [1]: https://github.com/torvalds/linux/commit/36e2c7421f02a22f71c9283e55fdb672a9eb58e7#diff-70c49af2ed5805fc1406ed6e6532d6a029ada1abd90cca6442711b9cecd4d523
>> [2]: https://github.com/torvalds/linux/blob/master/drivers/base/firmware_loader/main.c#L831
>> [3]: https://github.com/torvalds/linux/blob/master/fs/read_write.c#L1257
>> [4]: https://github.com/torvalds/linux/blob/master/fs/splice.c#L753
> kernel development is on git.kernel.org, not github :)
I use it because it is easier on the eyes when looking at diffs :D
But I'll be sure to use git.kernel.org from now on if that is what is 
preferred!
>
> thanks,
>
> greg k-h
Thanks,
Sid

[1]: 
https://android.googlesource.com/platform/system/core/+/refs/heads/master/init/firmware_handler.cpp#55