[Devel] [PATCH vz7 40/46] fuse: device fd clone

[Maxim Patlasov]

Backport from ml:

commit 00c570f4ba43ae73b41fa0a2269c3b0ac20386ef
Author: Miklos Szeredi <mszeredi at suse.cz>
Date:   Wed Jul 1 16:26:08 2015 +0200

    fuse: device fd clone

    Allow an open fuse device to be "cloned".  Userspace can create a clone by:

          newfd = open("/dev/fuse", O_RDWR)
          ioctl(newfd, FUSE_DEV_IOC_CLONE, &oldfd);

    At this point newfd will refer to the same fuse connection as oldfd.

    Signed-off-by: Miklos Szeredi <mszeredi at suse.cz>
    Reviewed-by: Ashish Samant <ashish.samant at oracle.com>

Signed-off-by: Maxim Patlasov <mpatlasov at virtuozzo.com>
---
 Documentation/ioctl/ioctl-number.txt |    1 +
 fs/fuse/dev.c                        |   40 ++++++++++++++++++++++++++++++++++
 include/uapi/linux/fuse.h            |    3 +++
 3 files changed, 44 insertions(+)

diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
index cc47d4e..ddaa510 100644
--- a/Documentation/ioctl/ioctl-number.txt
+++ b/Documentation/ioctl/ioctl-number.txt
@@ -323,6 +323,7 @@ Code  Seq#(hex)	Include File		Comments
 0xDB	00-0F	drivers/char/mwave/mwavepub.h
 0xDD	00-3F	ZFCP device driver	see drivers/s390/scsi/
 					<mailto:aherrman at de.ibm.com>
+0xE5	00-3F	linux/fuse.h
 0xF3	00-3F	drivers/usb/misc/sisusbvga/sisusb.h	sisfb (in development)
 					<mailto:thomas at winischhofer.net>
 0xF4	00-1F	video/mbxfb.h		mbxfb
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 70694ed..c2aac08 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -2192,6 +2192,44 @@ static int fuse_dev_fasync(int fd, struct file *file, int on)
 	return fasync_helper(fd, file, on, &fc->iq.fasync);
 }
 
+static int fuse_device_clone(struct fuse_conn *fc, struct file *new)
+{
+	if (new->private_data)
+		return -EINVAL;
+
+	new->private_data = fuse_conn_get(fc);
+
+	return 0;
+}
+
+static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
+			   unsigned long arg)
+{
+	int err = -ENOTTY;
+
+	if (cmd == FUSE_DEV_IOC_CLONE) {
+		int oldfd;
+
+		err = -EFAULT;
+		if (!get_user(oldfd, (__u32 __user *) arg)) {
+			struct file *old = fget(oldfd);
+
+			err = -EINVAL;
+			if (old) {
+				struct fuse_conn *fc = fuse_get_conn(old);
+
+				if (fc) {
+					mutex_lock(&fuse_mutex);
+					err = fuse_device_clone(fc, file);
+					mutex_unlock(&fuse_mutex);
+				}
+				fput(old);
+			}
+		}
+	}
+	return err;
+}
+
 const struct file_operations fuse_dev_operations = {
 	.owner		= THIS_MODULE,
 	.llseek		= no_llseek,
@@ -2204,6 +2242,8 @@ const struct file_operations fuse_dev_operations = {
 	.poll		= fuse_dev_poll,
 	.release	= fuse_dev_release,
 	.fasync		= fuse_dev_fasync,
+	.unlocked_ioctl = fuse_dev_ioctl,
+	.compat_ioctl   = fuse_dev_ioctl,
 };
 EXPORT_SYMBOL_GPL(fuse_dev_operations);
 
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index cb3cd15..3262980 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -749,4 +749,7 @@ struct fuse_notify_inval_files_out {
 	__u64	ino;
 };
 
+/* Device ioctls: */
+#define FUSE_DEV_IOC_CLONE	_IOR(229, 0, uint32_t)
+
 #endif /* _LINUX_FUSE_H */