求助Linux大牛！帮忙注释下文件系统中的fcntl.c函数

[laj0600310219]

代码接上一贴：

case F_SETFD:
err = 0;
set_close_on_exec(fd, arg & FD_CLOEXEC);
break;
case F_GETFL:
err = filp->f_flags;
break;
case F_SETFL:
err = setfl(fd, filp, arg);
break;
case F_GETLK:
err = fcntl_getlk(filp, (struct flock __user *) arg);
break;
case F_SETLK:
case F_SETLKW:
err = fcntl_setlk(fd, filp, cmd, (struct flock __user *) arg);
break;
case F_GETOWN:
/*
* XXX If f_owner is a process group, the
* negative return value will get converted
* into an error. Oops. If we keep the
* current syscall conventions, the only way
* to fix this will be in libc.
*/
err = f_getown(filp);
force_successful_syscall_return();
break;
case F_SETOWN:
err = f_setown(filp, arg, 1);
break;
case F_GETSIG:
err = filp->f_owner.signum;
break;
case F_SETSIG:
/* arg == 0 restores default behaviour. */
if (!valid_signal(arg)) {
break;
}
err = 0;
filp->f_owner.signum = arg;
break;
case F_GETLEASE:
err = fcntl_getlease(filp);
break;
case F_SETLEASE:
err = fcntl_setlease(fd, filp, arg);
break;
case F_NOTIFY:
err = fcntl_dirnotify(fd, filp, arg);
break;
default:
break;
}
return err;
}

SYSCALL_DEFINE3(fcntl, unsigned int, fd, unsigned int, cmd, unsigned long, arg)
{
struct file *filp;
long err = -EBADF;

filp = fget(fd);
if (!filp)
goto out;

err = security_file_fcntl(filp, cmd, arg);
if (err) {
fput(filp);
return err;
}

err = do_fcntl(fd, cmd, arg, filp);

fput(filp);
out:
return err;
}

#if BITS_PER_LONG == 32
SYSCALL_DEFINE3(fcntl64, unsigned int, fd, unsigned int, cmd,
unsigned long, arg)
{
struct file * filp;
long err;

err = -EBADF;
filp = fget(fd);
if (!filp)
goto out;

err = security_file_fcntl(filp, cmd, arg);
if (err) {
fput(filp);
return err;
}
err = -EBADF;

switch (cmd) {
case F_GETLK64:
err = fcntl_getlk64(filp, (struct flock64 __user *) arg);
break;
case F_SETLK64:
case F_SETLKW64:
err = fcntl_setlk64(fd, filp, cmd,
(struct flock64 __user *) arg);
break;
default:
err = do_fcntl(fd, cmd, arg, filp);
break;
}
fput(filp);
out:
return err;
}
#endif

/* Table to convert sigio signal codes into poll band bitmaps */

static const long band_table[NSIGPOLL] = {
POLLIN | POLLRDNORM, /* POLL_IN */
POLLOUT | POLLWRNORM | POLLWRBAND, /* POLL_OUT */
POLLIN | POLLRDNORM | POLLMSG, /* POLL_MSG */
POLLERR, /* POLL_ERR */
POLLPRI | POLLRDBAND, /* POLL_PRI */
POLLHUP | POLLERR /* POLL_HUP */
};

static inline int sigio_perm(struct task_struct *p,
struct fown_struct *fown, int sig)
{
const struct cred *cred;
int ret;

rcu_read_lock();
cred = __task_cred(p);
ret = ((fown->euid == 0 ||
fown->euid == cred->suid || fown->euid == cred->uid ||
fown->uid == cred->suid || fown->uid == cred->uid) &&
!security_file_send_sigiotask(p, fown, sig));
rcu_read_unlock();
return ret;
}

static void send_sigio_to_task(struct task_struct *p,
struct fown_struct *fown,
int fd,
int reason)
{
if (!sigio_perm(p, fown, fown->signum))
return;

switch (fown->signum) {
siginfo_t si;
default:
/* Queue a rt signal with the appropriate fd as its
value. We use SI_SIGIO as the source, not
SI_KERNEL, since kernel signals always get
delivered even if we can't queue. Failure to
queue in this case _should_ be reported; we fall
back to SIGIO in that case. --sct */
si.si_signo = fown->signum;
si.si_errno = 0;
si.si_code = reason;
/* Make sure we are called with one of the POLL_*
reasons, otherwise we could leak kernel stack into
userspace. */
BUG_ON((reason & __SI_MASK) != __SI_POLL);
if (reason - POLL_IN >= NSIGPOLL)
si.si_band = ~0L;
else
si.si_band = band_table[reason - POLL_IN];
si.si_fd = fd;
if (!group_send_sig_info(fown->signum, &si, p))
break;
/* fall-through: fall back on the old plain SIGIO signal */
case 0:
group_send_sig_info(SIGIO, SEND_SIG_PRIV, p);
}
}

void send_sigio(struct fown_struct *fown, int fd, int band)
{
struct task_struct *p;
enum pid_type type;
struct pid *pid;

read_lock(&fown->lock);
type = fown->pid_type;
pid = fown->pid;
if (!pid)
goto out_unlock_fown;

read_lock(&tasklist_lock);
do_each_pid_task(pid, type, p) {
send_sigio_to_task(p, fown, fd, band);
} while_each_pid_task(pid, type, p);
read_unlock(&tasklist_lock);
out_unlock_fown:
read_unlock(&fown->lock);
}

static void send_sigurg_to_task(struct task_struct *p,
struct fown_struct *fown)
{
if (sigio_perm(p, fown, SIGURG))
group_send_sig_info(SIGURG, SEND_SIG_PRIV, p);
}

int send_sigurg(struct fown_struct *fown)
{
struct task_struct *p;
enum pid_type type;
struct pid *pid;
int ret = 0;

read_lock(&fown->lock);
type = fown->pid_type;
pid = fown->pid;
if (!pid)
goto out_unlock_fown;

ret = 1;

read_lock(&tasklist_lock);
do_each_pid_task(pid, type, p) {
send_sigurg_to_task(p, fown);
} while_each_pid_task(pid, type, p);
read_unlock(&tasklist_lock);
out_unlock_fown:
read_unlock(&fown->lock);
return ret;
}

static DEFINE_RWLOCK(fasync_lock);
static struct kmem_cache *fasync_cache __read_mostly;

/*
* fasync_helper() is used by almost all character device drivers
* to set up the fasync queue. It returns negative on error, 0 if it did
* no changes and positive if it added/deleted the entry.
*/
int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fapp)
{
struct fasync_struct *fa, **fp;
struct fasync_struct *new = NULL;
int result = 0;

if (on) {
new = kmem_cache_alloc(fasync_cache, GFP_KERNEL);
if (!new)
return -ENOMEM;
}

/*
* We need to take f_lock first since it's not an IRQ-safe
* lock.
*/
spin_lock(&filp->f_lock);
write_lock_irq(&fasync_lock);
for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) {
if (fa->fa_file == filp) {
if(on) {
fa->fa_fd = fd;
kmem_cache_free(fasync_cache, new);
} else {
*fp = fa->fa_next;
kmem_cache_free(fasync_cache, fa);
result = 1;
}
goto out;
}
}

if (on) {
new->magic = FASYNC_MAGIC;
new->fa_file = filp;
new->fa_fd = fd;
new->fa_next = *fapp;
*fapp = new;
result = 1;
}
out:
if (on)
filp->f_flags |= FASYNC;
else
filp->f_flags &= ~FASYNC;
write_unlock_irq(&fasync_lock);
spin_unlock(&filp->f_lock);
return result;
}

EXPORT_SYMBOL(fasync_helper);

void __kill_fasync(struct fasync_struct *fa, int sig, int band)
{
while (fa) {
struct fown_struct * fown;
if (fa->magic != FASYNC_MAGIC) {
printk(KERN_ERR "kill_fasync: bad magic number in "
"fasync_struct!\n");
return;
}
fown = &fa->fa_file->f_owner;
/* Don't send SIGURG to processes which have not set a
queued signum: SIGURG has its own default signalling
mechanism. */
if (!(sig == SIGURG && fown->signum == 0))
send_sigio(fown, fa->fa_fd, band);
fa = fa->fa_next;
}
}

EXPORT_SYMBOL(__kill_fasync);

void kill_fasync(struct fasync_struct **fp, int sig, int band)
{
/* First a quick test without locking: usually
* the list is empty.
*/
if (*fp) {
read_lock(&fasync_lock);
/* reread *fp after obtaining the lock */
__kill_fasync(*fp, sig, band);
read_unlock(&fasync_lock);
}
}
EXPORT_SYMBOL(kill_fasync);

static int __init fasync_init(void)
{
fasync_cache = kmem_cache_create("fasync_cache",
sizeof(struct fasync_struct), 0, SLAB_PANIC, NULL);
return 0;
}

module_init(fasync_init)