From dfd78546c95330db2252e0d7e937a15ab5eddb4e Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Tue, 28 Oct 2025 09:45:50 +0100 Subject: pidfd: add a new supported_mask field Some of the future fields in struct pidfd_info can be optional. If the kernel has nothing to emit in that field, then it doesn't set the flag in the reply. This presents a problem: There is currently no way to know what mask flags the kernel supports since one can't always count on them being in the reply. Add a new PIDFD_INFO_SUPPORTED_MASK flag and field that the kernel can set in the reply. Userspace can use this to determine if the fields it requires from the kernel are supported. This also gives us a way to deprecate fields in the future, if that should become necessary. Link: https://patch.msgid.link/20251028-work-coredump-signal-v1-5-ca449b7b7aa0@kernel.org Reviewed-by: Alexander Mikhalitsyn Reviewed-by: Oleg Nesterov Signed-off-by: Christian Brauner --- include/uapi/linux/pidfd.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include/uapi') diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h index 6ccbabd9a68d..e05caa0e00fe 100644 --- a/include/uapi/linux/pidfd.h +++ b/include/uapi/linux/pidfd.h @@ -26,9 +26,11 @@ #define PIDFD_INFO_CGROUPID (1UL << 2) /* Always returned if available, even if not requested */ #define PIDFD_INFO_EXIT (1UL << 3) /* Only returned if requested. */ #define PIDFD_INFO_COREDUMP (1UL << 4) /* Only returned if requested. */ +#define PIDFD_INFO_SUPPORTED_MASK (1UL << 5) /* Want/got supported mask flags */ #define PIDFD_INFO_SIZE_VER0 64 /* sizeof first published struct */ #define PIDFD_INFO_SIZE_VER1 72 /* sizeof second published struct */ +#define PIDFD_INFO_SIZE_VER2 80 /* sizeof third published struct */ /* * Values for @coredump_mask in pidfd_info. @@ -94,6 +96,7 @@ struct pidfd_info { __s32 exit_code; __u32 coredump_mask; __u32 __spare1; + __u64 supported_mask; /* Mask flags that this kernel supports */ }; #define PIDFS_IOCTL_MAGIC 0xFF -- cgit v1.2.3