Hi, Arnd, Willy
> On Mon, May 29, 2023, at 21:54, Zhangjin Wu wrote:
> > use sys_llseek instead of sys_lseek to add 64bit seek even in 32bit
> > platforms.
> >
> > This code is based on sysdeps/unix/sysv/linux/lseek.c of glibc and
> > src/unistd/lseek.c of musl.
> >
> > Signed-off-by: Zhangjin Wu <falcon@xxxxxxxxxxx>
> > Signed-off-by: Willy Tarreau <w@xxxxxx>
> > ---
> > tools/include/nolibc/sys.h | 10 ++++++++++
> > 1 file changed, 10 insertions(+)
> >
> > diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
> > index 98cfa2f6d021..d0720af84b6d 100644
> > --- a/tools/include/nolibc/sys.h
> > +++ b/tools/include/nolibc/sys.h
> > @@ -672,7 +672,17 @@ int link(const char *old, const char *new)
> > static __attribute__((unused))
> > off_t sys_lseek(int fd, off_t offset, int whence)
> > {
> > +#if defined(__NR_llseek) || defined(__NR__llseek)
> > +#ifndef __NR__llseek
> > +#define __NR__llseek __NR_llseek
> > +#endif
> > + off_t result;
> > + return my_syscall5(__NR__llseek, fd, offset >> 32, offset, &result,
> > whence) ?: result;
> > +#elif defined(__NR_lseek)
> > return my_syscall3(__NR_lseek, fd, offset, whence);
> > +#else
> > +#error None of __NR_lseek, __NR_llseek nor __NR__llseek defined,
> > cannot implement sys_lseek()
> > +#endif
> > }
>
> This is not technically wrong, but I think a different approach
> would be clearer: Instead of having a sys_lseek() that works
> differently depending on the macros, why not define the low-level
> helpers to match the kernel arguments like
>
> static inline __attribute__((unused))
> __kernel_loff_t sys_lseek(int fd, __kernel_loff_t offset, int whence)
> {
> #ifdef __NR__llseek
> __kernel_loff_t result;
> return my_syscall5(__NR__llseek, fd, offset >> 32, offset, &result, whence) ?: result;
> #else
>
> #endif
> }
>
> static inline __attribute__((unused))
> __kernel_off_t sys_lseek(int fd, __kernel_off_t offset, int whence)
> {
> #ifdef __NR_lseek
> return my_syscall3(__NR_lseek, fd, offset, whence);
> #else
> return -ENOSYS;
> #endif
> }
>
> And then do the selection inside of the actual lseek,
> something like
>
> static __attribute__((unused))
> off_t lseek(int fd, off_t offset, int whence)
> {
> off_t ret = -ENOSYS;
>
> if (BITS_PER_LONG == 32)
> ret = sys_llseek(fd, offset, whence);
>
> if (ret == -ENOSYS)
> ret = sys_lseek(fd, offset, whence);
>
> if (ret < 0) {
> SET_ERRNO(-ret);
> ret = -1;
> }
> return ret;
>
> }
Yes, It is clearer, thanks. will learn carefully about the kernel types.
>
> For the loff_t selection, there is no real need to handle the
> fallback, so this could just be an if()/else to select 32-bit
> or 64-bit, but for the time_t ones the fallback is required
> for pre-5.6 kernels.
>
Ok, will test it on the pre-5.6 versions too.
Hi, Willy, what's your suggestion about the oldest kernel versions we plan to support? ;-)
Best regards,
Zhangjin
> Arnd
