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pidfd: add a new supported_mask field

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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 <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2025-10-28 09:45:50 +01:00
parent d8fc51d8fa
commit dfd78546c9
2 changed files with 19 additions and 1 deletions
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3
include/uapi/linux/pidfd.h
View file

@ -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