Re: [PATCH v5 liburing 0/3] Implement the kernel style return value

[Jens Axboe <axboe@kernel.dk>]

On 10/3/21 9:34 AM, Ammar Faizi wrote:
> Hi Jens,
> 
> This is the v5 of the kernel style return value implementation for
> liburing.
> 
> The main purpose of these changes is to make it possible to remove
> the dependency of `errno` variable in the liburing C sources. If we
> can land this on liburing, we will start working on adding support
> build liburing without libc.
> 
> Currently, we expose these functions to userland:
>   1) `__sys_io_uring_register`
>   2) `__sys_io_uring_setup`
>   3) `__sys_io_uring_enter2`
>   4) `__sys_io_uring_enter`
> 
> The tests in `test/io_uring_{enter,register,setup}.c` are the examples
> of it. Since the userland needs to check the `errno` value to use them
> properly, this means those functions always depend on libc. So we
> cannot change their behavior. Don't touch them all, this ensures the
> changes only affect liburing internal and no visible functionality
> changes for the users.
> 
> Then we introduce new functions with the same name (with extra
> underscore as prefix, 4 underscores):
>   1) `____sys_io_uring_register`
>   2) `____sys_io_uring_setup`
>   3) `____sys_io_uring_enter2`
>   4) `____sys_io_uring_enter`
> 
> These functions do not use `errno` variable *on the caller*, they use
> the kernel style return value (return a negative value of error code
> when errors).
> 
> These functions are defined as `static inline` in `src/syscall.h`.
> They are just a wrapper to make sure liburing internal sources do not
> touch `errno` variable from C files directly. We need to make C files
> not to touch the `errno` variable to support build without libc.
> 
> To completely remove the `errno` variable dependency from liburing C
> files. We wrap all syscalls in a kernel style return value as well.
> 
> Currently we have 5 other syscalls in liburing. We wrapped all of
> them as these 5 functions:
>   1) `uring_mmap`
>   2) `uring_munmap`
>   3) `uring_madvise`
>   4) `uring_getrlimit`
>   5) `uring_setrlimit`
> 
> All of them are `static inline` and will return a negative value of
> error code in case error happens.
> 
> Extra new helpers:
>   1) `ERR_PTR()`
>   2) `PTR_ERR()`
>   3) `IS_ERR()`
> 
> These helpers are used to deal with syscalls that return a pointer.
> Currently only `uring_mmap()` that depends on these.

Thanks, let's give this a go. I've applied the 3 patches.

-- 
Jens Axboe