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lib: os: Add refcounting to fdtable entries

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Use proper refcounting instead of magic value in obj field
when checking whether the fd is still in use. This will make
sure that if fd is shared between two threads, we do not
release it too soon.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
This commit is contained in:
Jukka Rissanen 2020-06-02 15:18:42 +03:00 committed by Andrew Boie
parent 1e9ae21084
commit 8b578bdceb
1 changed files with 43 additions and 16 deletions
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59
lib/os/fdtable.c
View file

@ -19,18 +19,14 @@
#include <sys/fdtable.h>
#include <sys/speculation.h>
#include <syscall_handler.h>
#include <sys/atomic.h>
struct fd_entry {
void *obj;
const struct fd_op_vtable *vtable;
atomic_t refcount;
};
/* A few magic values for fd_entry::obj used in the code. */
#define FD_OBJ_RESERVED (void *)1
#define FD_OBJ_STDIN (void *)0x10
#define FD_OBJ_STDOUT (void *)0x11
#define FD_OBJ_STDERR (void *)0x12
#ifdef CONFIG_POSIX_API
static const struct fd_op_vtable stdinout_fd_op_vtable;
#endif
@ -38,24 +34,53 @@ static const struct fd_op_vtable stdinout_fd_op_vtable;
static struct fd_entry fdtable[CONFIG_POSIX_MAX_FDS] = {
#ifdef CONFIG_POSIX_API
/*
* Predefine entries for stdin/stdout/stderr. Object pointer
* is unused and just should be !0 (random different values
* are used to posisbly help with debugging).
* Predefine entries for stdin/stdout/stderr.
*/
{FD_OBJ_STDIN, &stdinout_fd_op_vtable},
{FD_OBJ_STDOUT, &stdinout_fd_op_vtable},
{FD_OBJ_STDERR, &stdinout_fd_op_vtable},
{
/* STDIN */
.vtable = &stdinout_fd_op_vtable,
.refcount = ATOMIC_INIT(1)
},
{
/* STDOUT */
.vtable = &stdinout_fd_op_vtable,
.refcount = ATOMIC_INIT(1)
},
{
/* STDERR */
.vtable = &stdinout_fd_op_vtable,
.refcount = ATOMIC_INIT(1)
},
#endif
};
static K_MUTEX_DEFINE(fdtable_lock);
static int z_fd_ref(int fd)
{
return atomic_inc(&fdtable[fd].refcount) + 1;
}
static int z_fd_unref(int fd)
{
int old_rc = atomic_dec(&fdtable[fd].refcount);
if (old_rc != 1) {
return old_rc - 1;
}
fdtable[fd].obj = NULL;
fdtable[fd].vtable = NULL;
return 0;
}
static int _find_fd_entry(void)
{
int fd;
for (fd = 0; fd < ARRAY_SIZE(fdtable); fd++) {
if (fdtable[fd].obj == NULL) {
if (!atomic_get(&fdtable[fd].refcount)) {
return fd;
}
}
@ -73,7 +98,7 @@ static int _check_fd(int fd)
fd = k_array_index_sanitize(fd, ARRAY_SIZE(fdtable));
if (fdtable[fd].obj == NULL) {
if (!atomic_get(&fdtable[fd].refcount)) {
errno = EBADF;
return -1;
}
@ -122,7 +147,8 @@ int z_reserve_fd(void)
fd = _find_fd_entry();
if (fd >= 0) {
/* Mark entry as used, z_finalize_fd() will fill it in. */
fdtable[fd].obj = FD_OBJ_RESERVED;
fdtable[fd].obj = NULL;
fdtable[fd].vtable = NULL;
}
k_mutex_unlock(&fdtable_lock);
@ -145,12 +171,13 @@ void z_finalize_fd(int fd, void *obj, const struct fd_op_vtable *vtable)
#endif
fdtable[fd].obj = obj;
fdtable[fd].vtable = vtable;
(void)z_fd_ref(fd);
}
void z_free_fd(int fd)
{
/* Assumes fd was already bounds-checked. */
fdtable[fd].obj = NULL;
(void)z_fd_unref(fd);
}
int z_alloc_fd(void *obj, const struct fd_op_vtable *vtable)