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Subject[RFC][PATCH] fcntl: F_[SG]ETOWN_TID
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Date
In order to direct the SIGIO signal to a particular thread of a
multi-threaded application we cannot, like suggested by the manpage, put
a TID into the regular fcntl(F_SETOWN) call. It will still be send to
the whole process of which that thread is part.

Since people do want to properly direct SIGIO we introduce F_SETOWN_TID,
which functions similarly to F_SETOWN, except positive arguments are
interpreted as TIDs and negative arguments are interpreted as PIDs.

This extension is fully bug compatible with the old F_GETOWN
implementation in that F_GETOWN_TID will be troubled by the negative
return value for PIDs similarly to F_GETOWN's trouble with process
groups.

[ compile tested only so far ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
arch/parisc/include/asm/fcntl.h | 2 +
fs/fcntl.c | 64 +++++++++++++++++++++++++++++++++-----
include/asm-generic/fcntl.h | 4 ++
include/linux/fs.h | 11 +++++-
net/socket.c | 2 +-
5 files changed, 71 insertions(+), 12 deletions(-)
diff --git a/arch/parisc/include/asm/fcntl.h b/arch/parisc/include/asm/fcntl.h
index 1e1c824..5d5235a 100644
--- a/arch/parisc/include/asm/fcntl.h
+++ b/arch/parisc/include/asm/fcntl.h
@@ -28,6 +28,8 @@
#define F_SETOWN 12 /* for sockets. */
#define F_SETSIG 13 /* for sockets. */
#define F_GETSIG 14 /* for sockets. */
+#define F_GETOWN_TID 15
+#define F_SETOWN_TID 16

/* for posix fcntl() and lockf() */
#define F_RDLCK 01
diff --git a/fs/fcntl.c b/fs/fcntl.c
index ae41308..8d0b7f9 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -197,13 +197,15 @@ static int setfl(int fd, struct file * filp, unsigned long arg)
}

static void f_modown(struct file *filp, struct pid *pid, enum pid_type type,
- int force)
+ int flags)
{
write_lock_irq(&filp->f_owner.lock);
- if (force || !filp->f_owner.pid) {
+ if ((flags & FF_SETOWN_FORCE) || !filp->f_owner.pid) {
put_pid(filp->f_owner.pid);
filp->f_owner.pid = get_pid(pid);
filp->f_owner.pid_type = type;
+ filp->f_owner.task_only =
+ (type == PIDTYPE_PID && (flags & FF_SETOWN_TID));

if (pid) {
const struct cred *cred = current_cred();
@@ -215,7 +217,7 @@ static void f_modown(struct file *filp, struct pid *pid, enum pid_type type,
}

int __f_setown(struct file *filp, struct pid *pid, enum pid_type type,
- int force)
+ int flags)
{
int err;

@@ -223,12 +225,12 @@ int __f_setown(struct file *filp, struct pid *pid, enum pid_type type,
if (err)
return err;

- f_modown(filp, pid, type, force);
+ f_modown(filp, pid, type, flags);
return 0;
}
EXPORT_SYMBOL(__f_setown);

-int f_setown(struct file *filp, unsigned long arg, int force)
+int f_setown(struct file *filp, unsigned long arg, int flags)
{
enum pid_type type;
struct pid *pid;
@@ -241,7 +243,7 @@ int f_setown(struct file *filp, unsigned long arg, int force)
}
rcu_read_lock();
pid = find_vpid(who);
- result = __f_setown(filp, pid, type, force);
+ result = __f_setown(filp, pid, type, flags);
rcu_read_unlock();
return result;
}
@@ -263,6 +265,40 @@ pid_t f_getown(struct file *filp)
return pid;
}

+static int f_setown_tid(struct file *filp, unsigned long arg)
+{
+ int flags = FF_SETOWN_FORCE;
+ struct pid *pid;
+ int who = arg;
+ int ret = 0;
+
+ if (who < 0)
+ who = -who;
+ else
+ flags |= FF_SETOWN_TID;
+
+ rcu_read_lock();
+ pid = find_vpid(who);
+ ret = __f_setown(filp, pid, PIDTYPE_PID, flags);
+ rcu_read_unlock();
+
+ return ret;
+}
+
+static pid_t f_getown_tid(struct file *filp)
+{
+ pid_t tid;
+
+ read_lock(&filp->f_owner.lock);
+ tid = pid_vnr(filp->f_owner.pid);
+ if (filp->f_owner.pid_type == PIDTYPE_PGID)
+ tid = 0;
+ if (!filp->f_owner.task_only)
+ tid = -tid;
+ read_unlock(&filp->f_owner.lock);
+ return tid;
+}
+
static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
struct file *filp)
{
@@ -311,7 +347,14 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
force_successful_syscall_return();
break;
case F_SETOWN:
- err = f_setown(filp, arg, 1);
+ err = f_setown(filp, arg, FF_SETOWN_FORCE);
+ break;
+ case F_GETOWN_TID:
+ err = f_getown_tid(filp);
+ force_successful_syscall_return();
+ break;
+ case F_SETOWN_TID:
+ err = f_setown_tid(filp, arg);
break;
case F_GETSIG:
err = filp->f_owner.signum;
@@ -431,6 +474,7 @@ static void send_sigio_to_task(struct task_struct *p,
int fd,
int reason)
{
+ int (*send_sig)(int, struct siginfo *, struct task_struct *);
/*
* F_SETSIG can change ->signum lockless in parallel, make
* sure we read it once and use the same value throughout.
@@ -440,6 +484,8 @@ static void send_sigio_to_task(struct task_struct *p,
if (!sigio_perm(p, fown, signum))
return;

+ send_sig = fown->task_only ? send_sig_info : group_send_sig_info;
+
switch (signum) {
siginfo_t si;
default:
@@ -461,11 +507,11 @@ static void send_sigio_to_task(struct task_struct *p,
else
si.si_band = band_table[reason - POLL_IN];
si.si_fd = fd;
- if (!group_send_sig_info(signum, &si, p))
+ if (!send_sig(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);
+ send_sig(SIGIO, SEND_SIG_PRIV, p);
}
}

diff --git a/include/asm-generic/fcntl.h b/include/asm-generic/fcntl.h
index 4d3e483..d7906b8 100644
--- a/include/asm-generic/fcntl.h
+++ b/include/asm-generic/fcntl.h
@@ -73,6 +73,10 @@
#define F_SETSIG 10 /* for sockets. */
#define F_GETSIG 11 /* for sockets. */
#endif
+#ifndef F_SETOWN_TID
+#define F_SETOWN_TID 12
+#define F_GETOWN_TID 13
+#endif

/* for F_[GET|SET]FL */
#define FD_CLOEXEC 1 /* actually anything with low bit set goes */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0872372..42697e7 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -872,6 +872,7 @@ struct fown_struct {
rwlock_t lock; /* protects pid, uid, euid fields */
struct pid *pid; /* pid or -pgrp where SIGIO should be sent */
enum pid_type pid_type; /* Kind of process group SIGIO should be sent to */
+ bool task_only; /* task or group signal */
uid_t uid, euid; /* uid/euid of process setting the owner */
int signum; /* posix.1b rt signal to be delivered on IO */
};
@@ -1291,8 +1292,14 @@ extern void kill_fasync(struct fasync_struct **, int, int);
/* only for net: no internal synchronization */
extern void __kill_fasync(struct fasync_struct *, int, int);

-extern int __f_setown(struct file *filp, struct pid *, enum pid_type, int force);
-extern int f_setown(struct file *filp, unsigned long arg, int force);
+/*
+ * setown flags
+ */
+#define FF_SETOWN_FORCE 1
+#define FF_SETOWN_TID 2
+
+extern int __f_setown(struct file *filp, struct pid *, enum pid_type, int flags);
+extern int f_setown(struct file *filp, unsigned long arg, int flags);
extern void f_delown(struct file *filp);
extern pid_t f_getown(struct file *filp);
extern int send_sigurg(struct fown_struct *fown);
diff --git a/net/socket.c b/net/socket.c
index 791d71a..ac57f8e 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -916,7 +916,7 @@ static long sock_ioctl(struct file *file, unsigned cmd, unsigned long arg)
err = -EFAULT;
if (get_user(pid, (int __user *)argp))
break;
- err = f_setown(sock->file, pid, 1);
+ err = f_setown(sock->file, pid, FF_SETOWN_FORCE);
break;
case FIOGETOWN:
case SIOCGPGRP:



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