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@tinylab.org Signed-off-by: Willy Tarreau w@1wt.eu
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