3752 want more verifiable dbuf user eviction
Submitted by:   Justin Gibbs <justing@spectralogic.com>
Submitted by:   Will Andrews <willa@spectralogic.com>

@@ -43,10 +43,13 @@
 
 struct dsl_dataset;
 struct dsl_dir;
 struct dsl_pool;
 
+#define DS_HAS_PHYS(ds) \
+        ((ds)->ds_dbuf != NULL && (ds)->ds_dbuf->db_data != NULL)
+
 #define DS_FLAG_INCONSISTENT    (1ULL<<0)
 #define DS_IS_INCONSISTENT(ds)  \
         ((ds)->ds_phys->ds_flags & DS_FLAG_INCONSISTENT)
 /*
  * Note: nopromote can not yet be set, but we want support for it in this

@@ -109,15 +112,24 @@
         uint64_t ds_props_obj;          /* DMU_OT_DSL_PROPS for snaps */
         uint64_t ds_userrefs_obj;       /* DMU_OT_USERREFS */
         uint64_t ds_pad[5]; /* pad out to 320 bytes for good measure */
 } dsl_dataset_phys_t;
 
+typedef struct dsl_dataset_dbuf {
+        uint8_t dsdb_pad[offsetof(dmu_buf_t, db_data)];
+        dsl_dataset_phys_t *dsdb_data;
+} dsl_dataset_dbuf_t;
+
 typedef struct dsl_dataset {
+        dmu_buf_user_t db_evict;
+
         /* Immutable: */
         struct dsl_dir *ds_dir;
-        dsl_dataset_phys_t *ds_phys;
-        dmu_buf_t *ds_dbuf;
+        union {
+                dmu_buf_t *ds_dmu_db;
+                dsl_dataset_dbuf_t *ds_db;
+        } ds_db_u;
         uint64_t ds_object;
         uint64_t ds_fsid_guid;
 
         /* only used in syncing context, only valid for non-snapshots: */
         struct dsl_dataset *ds_prev;

@@ -161,10 +173,23 @@
 
         /* Protected by ds_lock; keep at end of struct for better locality */
         char ds_snapname[MAXNAMELEN];
 } dsl_dataset_t;
 
+/* See sys/dmu.h:dmu_buf_user_t for why we have these. */
+#define ds_dbuf ds_db_u.ds_dmu_db
+#define ds_phys ds_db_u.ds_db->dsdb_data
+
+struct dsl_ds_destroyarg {
+        dsl_dataset_t *ds;              /* ds to destroy */
+        dsl_dataset_t *rm_origin;       /* also remove our origin? */
+        boolean_t is_origin_rm;         /* set if removing origin snap */
+        boolean_t defer;                /* destroy -d requested? */
+        boolean_t releasing;            /* destroying due to release? */
+        boolean_t need_prep;            /* do we need to retry due to EBUSY? */
+};
+
 /*
  * The max length of a temporary tag prefix is the number of hex digits
  * required to express UINT64_MAX plus one for the hyphen.
  */
 #define MAX_TAG_PREFIX_LEN      17