[PATCH 21/33] TCMU PR: add a func to update PR info on TCMU dev

[Zhu Lingshan]

This patch  added a function tcmu_pr_info_replace() which can
help update Persistent Reservation information stored on a
TCMU device. It will generate a new string based on the provided
struct tcmu_pr_info struct, then write it to the device.For example,
If we are using RBD, it will update PR info to RBD meatada.

Signed-off-by: Zhu Lingshan <ls...@suse.com>
---
 drivers/target/target_core_user.c | 43 +++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/drivers/target/target_core_user.c 
b/drivers/target/target_core_user.c
index 4b426a9061b1..559e0d40d63b 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -111,6 +111,8 @@
 /* don't allow encoded PR info to exceed 8K */
 #define TCMU_PR_INFO_XATTR_MAX_SIZE 8192
 
+#define TCMU_PR_REG_MAX_RETRIES                5
+
 #define TCMU_PR_INFO_XATTR_ENCODED_SCSI2_RSV_MAXLEN            \
        (TCMU_PR_IT_NEXUS_MAXLEN + sizeof("\n"))
 
@@ -2648,6 +2650,47 @@ tcmu_execute_pr_register_existing(struct tcmu_pr_info 
*pr_info,
        return ret;
 }
 
+static int tcmu_pr_info_replace(struct tcmu_dev *udev,
+                               char *pr_xattr_old, int pr_xattr_len_old,
+                               struct tcmu_pr_info *pr_info_new)
+{
+       int rc;
+       char *pr_xattr_new = NULL;
+       int pr_xattr_len_new = 0;
+
+       WARN_ON(!pr_xattr_old || !pr_info_new);
+
+       /* bump seqnum prior to xattr write. Not rolled back on failure */
+       pr_info_new->seq++;
+       rc = tcmu_pr_info_encode(pr_info_new, &pr_xattr_new,
+                                &pr_xattr_len_new);
+
+       if (rc) {
+               pr_err("failed to encode PR xattr: %d\n", rc);
+               return rc;
+       }
+
+       if (pr_xattr_len_new > TCMU_PR_INFO_XATTR_MAX_SIZE) {
+               pr_err("unable to store oversize (%d) PR info: %s\n",
+                      pr_xattr_len_new, pr_xattr_new);
+               rc = -E2BIG;
+               goto err_xattr_new_free;
+       }
+
+       rc = tcmu_set_dev_pr_info(udev, pr_xattr_new);
+       if (rc) {
+               pr_err("failed to set PR xattr: %d\n", rc);
+               goto err_xattr_new_free;
+       }
+
+       pr_debug("successfully replaced PR info\n");
+       rc = 0;
+err_xattr_new_free:
+       kfree(pr_xattr_new);
+
+       return 0;
+}
+
 static int tcmu_configure_device(struct se_device *dev)
 {
        struct tcmu_dev *udev = TCMU_DEV(dev);
-- 
2.17.1