From c6269149cbf7053272d918101981869438ff7c1e Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Thu, 27 Jun 2024 16:11:39 +0200 Subject: [PATCH] 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: Jeff Layton Reviewed-by: Josef Bacik Reviewed-by: Alexander Mikhalitsyn Signed-off-by: Christian Brauner --- include/linux/cleanup.h | 13 ++++++++----- include/linux/file.h | 20 ++++++++++++++++++++ 2 files changed, 28 insertions(+), 5 deletions(-) diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h index c2d09bc4f9768..80c4181e194aa 100644 --- a/include/linux/cleanup.h +++ b/include/linux/cleanup.h @@ -63,17 +63,20 @@ #define __free(_name) __cleanup(__free_##_name) -#define __get_and_null_ptr(p) \ - ({ __auto_type __ptr = &(p); \ - __auto_type __val = *__ptr; \ - *__ptr = NULL; __val; }) +#define __get_and_null(p, nullvalue) \ + ({ \ + __auto_type __ptr = &(p); \ + __auto_type __val = *__ptr; \ + *__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) diff --git a/include/linux/file.h b/include/linux/file.h index 45d0f4800abd4..237931f20739f 100644 --- a/include/linux/file.h +++ b/include/linux/file.h @@ -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);