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

[Jens Axboe <axboe@kernel.dk>]

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