Re: [PATCH] windows: fix pread/pwrite

[Vincent Fu <vincentfu@gmail.com>]

On 5/8/25 1:35 PM, Jens Axboe wrote:
> On 5/8/25 11:31 AM, Vincent Fu wrote:
>> On Thu, May 8, 2025 at 1:18?PM Jens Axboe <axboe@kernel.dk> wrote:
>>>
>>> On 5/8/25 11:14 AM, Vincent Fu wrote:
>>>> The pread and pwrite functions for Windows posix emulation never actually seek
>>>> to the requested offset. Fix this so that the psync ioengine works correctly on
>>>> Windows.
>>>>
>>>> Signed-off-by: Vincent Fu <vincent.fu@samsung.com>
>>>> ---
>>>>   os/windows/posix.c | 10 ++++++++--
>>>>   1 file changed, 8 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/os/windows/posix.c b/os/windows/posix.c
>>>> index e3abf383..3e48c3ff 100644
>>>> --- a/os/windows/posix.c
>>>> +++ b/os/windows/posix.c
>>>> @@ -830,18 +830,24 @@ ssize_t pwrite(int fildes, const void *buf, size_t nbyte,
>>>>                off_t offset)
>>>>   {
>>>>        int64_t pos = _telli64(fildes);
>>>> -     ssize_t len = _write(fildes, buf, nbyte);
>>>> +     ssize_t len;
>>>>
>>>> +     _lseeki64(fildes, offset, SEEK_SET);
>>>> +     len = _write(fildes, buf, nbyte);
>>>>        _lseeki64(fildes, pos, SEEK_SET);
>>>> +
>>>>        return len;
>>>>   }
>>>>
>>>>   ssize_t pread(int fildes, void *buf, size_t nbyte, off_t offset)
>>>>   {
>>>>        int64_t pos = _telli64(fildes);
>>>> -     ssize_t len = read(fildes, buf, nbyte);
>>>> +     ssize_t len;
>>>>
>>>> +     _lseeki64(fildes, offset, SEEK_SET);
>>>> +     len = read(fildes, buf, nbyte);
>>>>        _lseeki64(fildes, pos, SEEK_SET);
>>>> +
>>>>        return len;
>>>>   }
>>>
>>> lol, how broken is that... Does windows have any offset read/write
>>> variants, or is lseek required?
>>>
>>> --
>>> Jens Axboe
>>>
>>
>> I could not find a better way to do this but I am hoping someone who
>> knows more about Windows than I do can weigh in. Sitsofe?
> 
> It's probably not a big deal. I did a quick search and doesn't seem like
> one exists for that.
> 

Ok thanks. I will go ahead with it then.

Vincent