Unverified Commit c6269149 authored by Christian Brauner's avatar Christian Brauner
Browse files

file: add take_fd() cleanup helper 

Add a helper that returns the file descriptor and ensures that the old
variable contains a negative value. This makes it easy to rely on
CLASS(get_unused_fd).

Link: https://lore.kernel.org/r/20240627-work-pidfs-v1-1-7e9ab6cc3bb1@kernel.org


Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Reviewed-by: default avatarJosef Bacik <josef@toxicpanda.com>
Reviewed-by: default avatarAlexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent ff2c570e

include/linux/cleanup.h

+8 −5
Original line number Diff line number Diff line
@@ -63,17 +63,20 @@ 


#define __free(_name)	__cleanup(__free_##_name)



#define __get_and_null_ptr(p) \

	({ __auto_type __ptr = &(p); \

#define __get_and_null(p, nullvalue)   \

	({                                  \

		__auto_type __ptr = &(p);   \

		__auto_type __val = *__ptr; \

	   *__ptr = NULL;  __val; })

		*__ptr = nullvalue;         \

		__val;                      \

	})



static inline __must_check

const volatile void * __must_check_fn(const volatile void *val)

{ return val; }



#define no_free_ptr(p) \

	((typeof(p)) __must_check_fn(__get_and_null_ptr(p)))

	((typeof(p)) __must_check_fn(__get_and_null(p, NULL)))



#define return_ptr(p)	return no_free_ptr(p)

include/linux/file.h

+20 −0
Original line number Diff line number Diff line
@@ -97,6 +97,26 @@ extern void put_unused_fd(unsigned int fd); 
DEFINE_CLASS(get_unused_fd, int, if (_T >= 0) put_unused_fd(_T),

	     get_unused_fd_flags(flags), unsigned flags)



/*

 * take_fd() will take care to set @fd to -EBADF ensuring that

 * CLASS(get_unused_fd) won't call put_unused_fd(). This makes it

 * easier to rely on CLASS(get_unused_fd):

 *

 * struct file *f;

 *

 * CLASS(get_unused_fd, fd)(O_CLOEXEC);

 * if (fd < 0)

 *         return fd;

 *

 * f = dentry_open(&path, O_RDONLY, current_cred());

 * if (IS_ERR(f))

 *         return PTR_ERR(fd);

 *

 * fd_install(fd, f);

 * return take_fd(fd);

 */

#define take_fd(fd) __get_and_null(fd, -EBADF)



extern void fd_install(unsigned int fd, struct file *file);



int receive_fd(struct file *file, int __user *ufd, unsigned int o_flags);