linux-kernel - Re: [PATCH] staging: android: ashmem: lseek failed due to no FMODE

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Date:   Thu, 6 Apr 2017 10:25:32 -0700
From:   Greg Hackmann <ghackmann@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     zhangshuxiaomi@...il.com, arve@...roid.com, riandrews@...roid.com,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        zhangshuxiao <zhangshuxiao@...omi.com>
Subject: Re: [PATCH] staging: android: ashmem: lseek failed due to no
 FMODE_LSEEK.

On 04/06/2017 10:08 AM, Greg KH wrote:
> On Thu, Apr 06, 2017 at 08:30:40AM -0700, Greg Hackmann wrote:
>> On 04/06/2017 07:30 AM, zhangshuxiaomi@...il.com wrote:
>>> From: zhangshuxiao <zhangshuxiao@...omi.com>
>>>
>>> vfs_llseek will check whether the file mode has
>>> FMODE_LSEEK, no return failure. But ashmem can be
>>> lseek, so add FMODE_LSEEK to ashmem file.
>>>
>>> Signed-off-by: Shuxiao Zhang <zhangshuxiao@...omi.com>
>>> Tested-by: Greg Hackmann <ghackmann@...gle.com>
>>> ---
>>>  drivers/staging/android/ashmem.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
>>> index 3f11332..e4530ac 100644
>>> --- a/drivers/staging/android/ashmem.c
>>> +++ b/drivers/staging/android/ashmem.c
>>> @@ -392,6 +392,7 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
>>>  			ret = PTR_ERR(vmfile);
>>>  			goto out;
>>>  		}
>>> +		vmfile->f_mode |= FMODE_LSEEK;
>>>  		asma->file = vmfile;
>>>  	}
>>>  	get_file(asma->file);
>>>
>>
>> This commit message is missing some important context.
>>
>> ashmem_llseek() passes the llseek() call through to the backing shmem file.
>> 91360b02ab48 ("ashmem: use vfs_llseek()") changed this from directly calling
>> the file's llseek() op into a VFS layer call.  This also adds a check for
>> the FMODE_LSEEK bit, so without that bit ashmem_llseek() now always fails
>> with -ESPIPE.
>>
>> I've tested that this patch fixes the regression on both hikey running AOSP
>> and User Mode Linux running Debian.
>
> Thanks for letting me know, I'll update the changelog a bit.  How far
> back does this patch need to go in stable kernel releases?
>
> thanks,
>
> greg k-h
>

3.18 and later.