On Thu, Oct 21, 2021 at 7:54 AM Alistair Francis <alistair.francis@xxxxxxxxxxxxxxxxxx> wrote: > > From: Alistair Francis <alistair.francis@xxxxxxx> > > This commit adds two futex syscall wrappers that are exposed to > userspace. > > Neither the kernel or glibc currently expose a futex wrapper, so > userspace is left performing raw syscalls. This has mostly been becuase > the overloading of one of the arguments makes it impossible to provide a > single type safe function. > > Until recently the single syscall has worked fine. With the introduction > of a 64-bit time_t futex call on 32-bit architectures, this has become > more complex. The logic of handling the two possible futex syscalls is > complex and often implemented incorrectly. > > This patch adds two futux syscall functions that correctly handle the > time_t complexity for userspace. > > This idea is based on previous discussions: https://lkml.org/lkml/2021/9/21/143 > > Signed-off-by: Alistair Francis <alistair.francis@xxxxxxx> This looks good to me, it addresses my earlier feedback, but I think we need others to look into the question of whether we want this to be a single function (as I suggested last time) or a pair of them (as you did). I just replied to your email about this at https://lore.kernel.org/lkml/CAK8P3a1CxFfHze6id1sQbQXV-x8DXkEdfqh51MwabzwhKAoTdQ@xxxxxxxxxxxxxx/ I added the futex maintainers and the linux-api list to Cc for them to reply. Full patch quoted below, no further comments from me. Arnd > --- > include/uapi/linux/futex_syscall.h | 81 ++++++++++++++++++++++++++++++ > 1 file changed, 81 insertions(+) > create mode 100644 include/uapi/linux/futex_syscall.h > > diff --git a/include/uapi/linux/futex_syscall.h b/include/uapi/linux/futex_syscall.h > new file mode 100644 > index 0000000000000..f84a0c68baf78 > --- /dev/null > +++ b/include/uapi/linux/futex_syscall.h > @@ -0,0 +1,81 @@ > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ > +#ifndef _UAPI_LINUX_FUTEX_SYSCALL_H > +#define _UAPI_LINUX_FUTEX_SYSCALL_H > + > +#include <asm/unistd.h> > +#include <errno.h> > +#include <linux/types.h> > +#include <linux/time_types.h> > +#include <sys/syscall.h> > + > +/** > + * futex_syscall_timeout() - __NR_futex/__NR_futex_time64 syscall wrapper > + * @uaddr: address of first futex > + * @op: futex op code > + * @val: typically expected value of uaddr, but varies by op > + * @timeout: an absolute struct timespec > + * @uaddr2: address of second futex for some ops > + * @val3: varies by op > + */ > +static inline int > +__kernel_futex_syscall_timeout(volatile u_int32_t *uaddr, int op, u_int32_t val, > + struct timespec *timeout, volatile u_int32_t *uaddr2, int val3) > +{ > +#if defined(__NR_futex_time64) > + if (sizeof(*timeout) != sizeof(struct __kernel_old_timespec)) { > + int ret = syscall(__NR_futex_time64, uaddr, op, val, timeout, uaddr2, val3); > + > + if (ret == 0 || errno != ENOSYS) > + return ret; > + } > +#endif > + > +#if defined(__NR_futex) > + if (sizeof(*timeout) == sizeof(struct __kernel_old_timespec)) > + return syscall(__NR_futex, uaddr, op, val, timeout, uaddr2, val3); > + > + if (timeout && timeout->tv_sec == (long)timeout->tv_sec) { > + struct __kernel_old_timespec ts32; > + > + ts32.tv_sec = (__kernel_long_t) timeout->tv_sec; > + ts32.tv_nsec = (__kernel_long_t) timeout->tv_nsec; > + > + return syscall(__NR_futex, uaddr, op, val, &ts32, uaddr2, val3); > + } else if (!timeout) { > + return syscall(__NR_futex, uaddr, op, val, NULL, uaddr2, val3); > + } > +#endif > + > + errno = ENOSYS; > + return -1; > +} > + > +/** > + * futex_syscall_nr_requeue() - __NR_futex/__NR_futex_time64 syscall wrapper > + * @uaddr: address of first futex > + * @op: futex op code > + * @val: typically expected value of uaddr, but varies by op > + * @nr_requeue: an op specific meaning > + * @uaddr2: address of second futex for some ops > + * @val3: varies by op > + */ > +static inline int > +__kernel_futex_syscall_nr_requeue(volatile u_int32_t *uaddr, int op, u_int32_t val, > + u_int32_t nr_requeue, volatile u_int32_t *uaddr2, int val3) > +{ > +#if defined(__NR_futex_time64) > + int ret = syscall(__NR_futex_time64, uaddr, op, val, nr_requeue, uaddr2, val3); > + > + if (ret == 0 || errno != ENOSYS) > + return ret; > +#endif > + > +#if defined(__NR_futex) > + return syscall(__NR_futex, uaddr, op, val, nr_requeue, uaddr2, val3); > +#endif > + > + errno = ENOSYS; > + return -1; > +} > + > +#endif /* _UAPI_LINUX_FUTEX_SYSCALL_H */ > -- > 2.31.1 >
