Re: [PATCH] filesetup: do not ask O_RDWR for read-only workload

[Vincent Fu <vincentfu@gmail.com>]

On 2/3/23 07:46, Jens Axboe wrote:
> On Feb 3, 2023, at 5:35 AM, Kanchan Joshi <joshi.k@samsung.com> wrote:
>>
>> Use O_RDONLY flag when read is requested on char-type files.
>>
>> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
>> ---
>>
>> Before this patch: unexpected permission-denial for unprivileged-user.
>>
>> $ ls -l /dev/ng0n1
>> cr--r--r-- 1 root root 242, 0 Feb  3 16:30 /dev/ng0n1
>>
>> $ ./fio -iodepth=1 -rw=randread -ioengine=io_uring_cmd -bs=4k -numjobs=1
>> -size=4k -cmd_type=nvme -filename=/dev/ng0n1 -name=t
>> t: (g=0): rw=randread, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T)
>> 4096B-4096B, ioengine=io_uring_cmd, iodepth=1
>> fio-3.33-71-g7d7a
>> Starting 1 process
>> fio: pid=131312, err=13/file:filesetup.c:805, func=open(/dev/ng0n1),
>> error=Permission denied
>>
>> filesetup.c | 5 +----
>> 1 file changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/filesetup.c b/filesetup.c
>> index 1d3cc5ad..d77b8ba4 100644
>> --- a/filesetup.c
>> +++ b/filesetup.c
>> @@ -768,10 +768,7 @@ open_again:
>>         else
>>             from_hash = file_lookup_open(f, flags);
>>     } else if (td_read(td)) {
>> -        if (f->filetype == FIO_TYPE_CHAR && !read_only)
>> -            flags |= O_RDWR;
>> -        else
>> -            flags |= O_RDONLY;
>> +        flags |= O_RDONLY;
> 
> This will break sg like interfaces, where a read is done by writing the command to the char device.
> 
> —
> Jens Axboe
> 

Kanchan, does it work if you run fio with the --readonly option?

Vincent