linux-kernel - [PATCH 06/18] osd_uld: API for retrieving osd devices from Kernel

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Message-Id: <1225817081-6017-1-git-send-email-bharrosh@panasas.com>
Date:	Tue,  4 Nov 2008 18:44:41 +0200
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Christie <michaelc@...wisc.edu>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Jeff Garzik <jeff@...zik.org>,
	open-osd ml <osd-dev@...n-osd.org>,
	linux-scsi <linux-scsi@...r.kernel.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>, Sami.Iren@...gate.com,
	Pete Wyckoff <pw@...d.com>
Subject: [PATCH 06/18] osd_uld: API for retrieving osd devices from Kernel

Kernel clients like osdfs can retrieve struct osd_dev(s)
by means of below API.

+ osduld_path_lookup() - given a path (e.g "/dev/osd0") locks and
returns the corresponding struct osd_dev, which is then needed
for subsequent libosd use.

+ osduld_put_device() - free up use of an osd_dev.

Devices can be shared by multiple clients. The osd_uld_device's
life time is governed by an embedded kref structure.

The osd_uld_device holds an extra reference to both it's
char-device and it's scsi_device, and will release these just
before the final deallocation.

There are three possible lock sources of the osd_uld_device
1. First and for most is the probe() function called by
  scsi-ml upon a successful login into a target. Released in release()
  when logout.
2. Second by user-mode file handles opened on the char-dev.
3. Third is here by Kernel users.
All three locks must be removed before the osd_uld_device is freed.

The MODULE has three lock sources as well:
1. scsi-ml at probe() time, removed after release(). (login/logout)
2. The user-mode file handles open/close.
3. Import symbols by client modules like osdfs.

TODO:
  This API is not enough for the pNFS-objects LD. A more versatile
  API will be needed. Proposed API could be:
  struct osd_dev *osduld_sysid_lookup(const char id[OSD_SYSTEMID_LEN]);

Signed-off-by: Boaz Harrosh <bharrosh@...asas.com>
---
 drivers/scsi/osd/osd_uld.c   |   52 ++++++++++++++++++++++++++++++++++++++++++
 include/scsi/osd_initiator.h |    5 ++++
 2 files changed, 57 insertions(+), 0 deletions(-)

diff --git a/drivers/scsi/osd/osd_uld.c b/drivers/scsi/osd/osd_uld.c
index 87b4540..0229301 100644
--- a/drivers/scsi/osd/osd_uld.c
+++ b/drivers/scsi/osd/osd_uld.c
@@ -42,6 +42,7 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <linux/namei.h>
 #include <linux/cdev.h>
 #include <linux/fs.h>
 #include <linux/module.h>
@@ -142,6 +143,57 @@ static const struct file_operations osd_fops = {
 	.unlocked_ioctl = osd_uld_ioctl,
 };
 
+struct osd_dev *osduld_path_lookup(const char *path)
+{
+	struct nameidata nd;
+	struct inode *inode;
+	struct cdev *cdev;
+	struct osd_uld_device *oud;
+	int error;
+
+	if (!path || !*path)
+		return ERR_PTR(-EINVAL);
+
+	error = path_lookup(path, LOOKUP_FOLLOW, &nd);
+	if (error)
+		return ERR_PTR(error);
+
+	inode = nd.path.dentry->d_inode;
+	error = -EINVAL; /* Not the right device e.g osd_uld_device */
+	if (!S_ISCHR(inode->i_mode))
+		goto out;
+
+	cdev = inode->i_cdev;
+	if (!cdev)
+		goto out;
+
+	/* The Magic wand. Is it our char-dev */
+	/* TODO: Support sg devices */
+	if (cdev->owner != THIS_MODULE)
+		goto out;
+
+	oud = container_of(cdev, struct osd_uld_device, cdev);
+
+	__uld_get(oud);
+	error = 0;
+
+out:
+	path_put(&nd.path);
+	return error ? ERR_PTR(error) : &oud->od;
+}
+EXPORT_SYMBOL(osduld_path_lookup);
+
+void osduld_put_device(struct osd_dev *od)
+{
+	if (od) {
+		struct osd_uld_device *oud = container_of(od,
+						struct osd_uld_device, od);
+
+		__uld_put(oud);
+	}
+}
+EXPORT_SYMBOL(osduld_put_device);
+
 /*
  * Scsi Device operations
  */
diff --git a/include/scsi/osd_initiator.h b/include/scsi/osd_initiator.h
index 24a70b7..0004df1 100644
--- a/include/scsi/osd_initiator.h
+++ b/include/scsi/osd_initiator.h
@@ -33,6 +33,11 @@ struct osd_dev {
 	unsigned def_timeout;
 };
 
+/* Retrieve/return osd_dev(s) for use by Kernel clients */
+struct osd_dev *osduld_path_lookup(const char *dev_name); /*Use IS_ERR/ERR_PTR*/
+void osduld_put_device(struct osd_dev *od);
+
+/* These are called by uld at probe time */
 void osd_dev_init(struct osd_dev *, struct scsi_device *scsi_dev);
 void osd_dev_fini(struct osd_dev *);
 
-- 
1.6.0.1

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