linux-stable/include/linux/fdtable.h
Al Viro 6319194ec5 Unify the primitives for file descriptor closing
Currently we have 3 primitives for removing an opened file from descriptor
table - pick_file(), __close_fd_get_file() and close_fd_get_file().  Their
calling conventions are rather odd and there's a code duplication for no
good reason.  They can be unified -

1) have __range_close() cap max_fd in the very beginning; that way
we don't need separate way for pick_file() to report being past the end
of descriptor table.

2) make {__,}close_fd_get_file() return file (or NULL) directly, rather
than returning it via struct file ** argument.  Don't bother with
(bogus) return value - nobody wants that -ENOENT.

3) make pick_file() return NULL on unopened descriptor - the only caller
that used to care about the distinction between descriptor past the end
of descriptor table and finding NULL in descriptor table doesn't give
a damn after (1).

4) lift ->files_lock out of pick_file()

That actually simplifies the callers, as well as the primitives themselves.
Code duplication is also gone...

Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2022-05-14 18:49:01 -04:00

134 lines
3.6 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
/*
* descriptor table internals; you almost certainly want file.h instead.
*/
#ifndef __LINUX_FDTABLE_H
#define __LINUX_FDTABLE_H
#include <linux/posix_types.h>
#include <linux/compiler.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
#include <linux/nospec.h>
#include <linux/types.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/atomic.h>
/*
* The default fd array needs to be at least BITS_PER_LONG,
* as this is the granularity returned by copy_fdset().
*/
#define NR_OPEN_DEFAULT BITS_PER_LONG
#define NR_OPEN_MAX ~0U
struct fdtable {
unsigned int max_fds;
struct file __rcu **fd; /* current fd array */
unsigned long *close_on_exec;
unsigned long *open_fds;
unsigned long *full_fds_bits;
struct rcu_head rcu;
};
static inline bool close_on_exec(unsigned int fd, const struct fdtable *fdt)
{
return test_bit(fd, fdt->close_on_exec);
}
static inline bool fd_is_open(unsigned int fd, const struct fdtable *fdt)
{
return test_bit(fd, fdt->open_fds);
}
/*
* Open file table structure
*/
struct files_struct {
/*
* read mostly part
*/
atomic_t count;
bool resize_in_progress;
wait_queue_head_t resize_wait;
struct fdtable __rcu *fdt;
struct fdtable fdtab;
/*
* written part on a separate cache line in SMP
*/
spinlock_t file_lock ____cacheline_aligned_in_smp;
unsigned int next_fd;
unsigned long close_on_exec_init[1];
unsigned long open_fds_init[1];
unsigned long full_fds_bits_init[1];
struct file __rcu * fd_array[NR_OPEN_DEFAULT];
};
struct file_operations;
struct vfsmount;
struct dentry;
#define rcu_dereference_check_fdtable(files, fdtfd) \
rcu_dereference_check((fdtfd), lockdep_is_held(&(files)->file_lock))
#define files_fdtable(files) \
rcu_dereference_check_fdtable((files), (files)->fdt)
/*
* The caller must ensure that fd table isn't shared or hold rcu or file lock
*/
static inline struct file *files_lookup_fd_raw(struct files_struct *files, unsigned int fd)
{
struct fdtable *fdt = rcu_dereference_raw(files->fdt);
if (fd < fdt->max_fds) {
fd = array_index_nospec(fd, fdt->max_fds);
return rcu_dereference_raw(fdt->fd[fd]);
}
return NULL;
}
static inline struct file *files_lookup_fd_locked(struct files_struct *files, unsigned int fd)
{
RCU_LOCKDEP_WARN(!lockdep_is_held(&files->file_lock),
"suspicious rcu_dereference_check() usage");
return files_lookup_fd_raw(files, fd);
}
static inline struct file *files_lookup_fd_rcu(struct files_struct *files, unsigned int fd)
{
RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
"suspicious rcu_dereference_check() usage");
return files_lookup_fd_raw(files, fd);
}
static inline struct file *lookup_fd_rcu(unsigned int fd)
{
return files_lookup_fd_rcu(current->files, fd);
}
struct file *task_lookup_fd_rcu(struct task_struct *task, unsigned int fd);
struct file *task_lookup_next_fd_rcu(struct task_struct *task, unsigned int *fd);
struct task_struct;
void put_files_struct(struct files_struct *fs);
int unshare_files(void);
struct files_struct *dup_fd(struct files_struct *, unsigned, int *) __latent_entropy;
void do_close_on_exec(struct files_struct *);
int iterate_fd(struct files_struct *, unsigned,
int (*)(const void *, struct file *, unsigned),
const void *);
extern int close_fd(unsigned int fd);
extern int __close_range(unsigned int fd, unsigned int max_fd, unsigned int flags);
extern struct file *close_fd_get_file(unsigned int fd);
extern int unshare_fd(unsigned long unshare_flags, unsigned int max_fds,
struct files_struct **new_fdp);
extern struct kmem_cache *files_cachep;
#endif /* __LINUX_FDTABLE_H */