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[173.79.40.147]) by smtp.gmail.com with ESMTPSA id x3-20020a05620a098300b00721b773b40asm9613951qkx.4.2023.02.07.08.16.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Feb 2023 08:16:44 -0800 (PST) Message-ID: Date: Tue, 7 Feb 2023 11:16:43 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH] filesetup: do not ask O_RDWR for read-only workload To: Jens Axboe , Kanchan Joshi Cc: fio@vger.kernel.org, vincent.fu@samsung.com References: <20230203123421.126720-1-joshi.k@samsung.com> <5B11C29F-19ED-4ADF-A900-F430608CC46C@kernel.dk> <20230206065251.GA19745@green5> <678ee3fe-5408-ca9c-f7f4-dc3134765b06@kernel.dk> Content-Language: en-US From: Vincent Fu In-Reply-To: <678ee3fe-5408-ca9c-f7f4-dc3134765b06@kernel.dk> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: fio@vger.kernel.org On 2/6/23 14:37, Jens Axboe wrote: > On 2/5/23 11:52?PM, Kanchan Joshi wrote: >> On Fri, Feb 03, 2023 at 10:26:15AM -0500, Vincent Fu wrote: >>> On 2/3/23 09:14, Jens Axboe wrote: >>>> On 2/3/23 7:08?AM, Vincent Fu wrote: >>>>> On 2/3/23 07:46, Jens Axboe wrote: >>>>>> On Feb 3, 2023, at 5:35 AM, Kanchan Joshi wrote: >>>>>>> >>>>>>> ?Use O_RDONLY flag when read is requested on char-type files. >>>>>>> >>>>>>> Signed-off-by: Kanchan Joshi >>>>>>> --- >>>>>>> >>>>>>> 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? >>>> >>>> I think we should just make it work. Conceptually, the patch is obviously >>>> fine, it just happens to break some oddball cases like sg/bsg. But maybe >>>> we just add a fio ioengine flag for that, like FIO_RO_NEEDS_RW_OPEN or >>>> something, where the engine can tell us if it needs a writeable open >>>> even or a read-only workload. >>>> >>>> Then generic_file_open() can use O_RDONLY for td_read(), except if the >>>> engine has FIO_RO_NEEDS_RW_OPEN set. >>>> >>> >>> Kanchan, can you try the diff below? It's also available at https://protect2.fireeye.com/v1/url?k=37173803-566c928b-3716b34c-74fe4860018a-aac6167af74310c3&q=1&e=3e678cf7-7d3f-487a-8a94-a9f0b41ca778&u=https%3A%2F%2Fgithub.com%2Fvincentkfu%2Ffio%2Ftree%2Frwopen >> >> Tried, this works, thanks! >> The patch looks good. Seems this flag can be added to libzbc engine too. >> That also treats the the char-type open in the same way. > > Thanks for testing - I've added it for libzbc as well. > The new flag only affects generic_file_open() but the libzbc ioengine has its own file open function. So the flag has no effect. Moreover libzbc uses the SG_IO ioctl even for character devices. So the code in libzbc_open_dev() (copied from generic_file_open) that opens character devices with O_RDWR is actually unnecessary. I've committed some patches to tidy things up. Vincent