From c62b758bae6af16fee94f556091fa74883a96b1e Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Thu, 9 May 2024 13:04:24 +0200 Subject: fcntl: add F_DUPFD_QUERY fcntl() Often userspace needs to know whether two file descriptors refer to the same struct file. For example, systemd uses this to filter out duplicate file descriptors in it's file descriptor store (cf. [1]) and vulkan uses it to compare dma-buf fds (cf. [2]). The only api we provided for this was kcmp() but that's not generally available or might be disallowed because it is way more powerful (allows ordering of file pointers, operates on non-current task) etc. So give userspace a simple way of comparing two file descriptors for sameness adding a new fcntl() F_DUDFD_QUERY. Link: https://github.com/systemd/systemd/blob/a4f0e0da3573a10bc5404142be8799418760b1d1/src/basic/fd-util.c#L517 [1] Link: https://gitlab.freedesktop.org/wlroots/wlroots/-/blob/master/render/vulkan/texture.c#L490 [2] Signed-off-by: Linus Torvalds [brauner: commit message] Signed-off-by: Christian Brauner --- include/uapi/linux/fcntl.h | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) (limited to 'include/uapi/linux') diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h index 282e90aeb163..c0bcc185fa48 100644 --- a/include/uapi/linux/fcntl.h +++ b/include/uapi/linux/fcntl.h @@ -8,6 +8,14 @@ #define F_SETLEASE (F_LINUX_SPECIFIC_BASE + 0) #define F_GETLEASE (F_LINUX_SPECIFIC_BASE + 1) +/* + * Request nofications on a directory. + * See below for events that may be notified. + */ +#define F_NOTIFY (F_LINUX_SPECIFIC_BASE + 2) + +#define F_DUPFD_QUERY (F_LINUX_SPECIFIC_BASE + 3) + /* * Cancel a blocking posix lock; internal use only until we expose an * asynchronous lock api to userspace: @@ -17,12 +25,6 @@ /* Create a file descriptor with FD_CLOEXEC set. */ #define F_DUPFD_CLOEXEC (F_LINUX_SPECIFIC_BASE + 6) -/* - * Request nofications on a directory. - * See below for events that may be notified. - */ -#define F_NOTIFY (F_LINUX_SPECIFIC_BASE+2) - /* * Set and get of pipe page size array */ -- cgit v1.2.3