[SCSI] osd_uld: API for retrieving osd devices from Kernel

Kernel clients like exofs 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 exofs.

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@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 63 insertions, 0 deletions

diff --git a/drivers/scsi/osd/osd_uld.c b/drivers/scsi/osd/osd_uld.c
index f6f9a99adaa6..cd4ca7cd9f75 100644
--- a/drivers/scsi/osd/osd_uld.c
+++ b/drivers/scsi/osd/osd_uld.c
@@ -173,6 +173,69 @@ 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 *uninitialized_var(oud);
+        int error;
+
+        if (!path || !*path) {
+                OSD_ERR("Mount with !path || !*path\n");
+                return ERR_PTR(-EINVAL);
+        }
+
+        error = path_lookup(path, LOOKUP_FOLLOW, &nd);
+        if (error) {
+                OSD_ERR("path_lookup of %s faild=>%d\n", path, 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)) {
+                OSD_DEBUG("!S_ISCHR()\n");
+                goto out;
+        }
+
+        cdev = inode->i_cdev;
+        if (!cdev) {
+                OSD_ERR("Before mounting an OSD Based filesystem\n");
+                OSD_ERR("  user-mode must open+close the %s device\n", path);
+                OSD_ERR("  Example: bash: echo < %s\n", path);
+                goto out;
+        }
+
+        /* The Magic wand. Is it our char-dev */
+        /* TODO: Support sg devices */
+        if (cdev->owner != THIS_MODULE) {
+                OSD_ERR("Error mounting %s - is not an OSD device\n", path);
+                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
  */