target: Minimize #include directives

Remove superfluous #include directives from the include/target/*.h
files. Add missing #include directives to other *.h and *.c files.
Use forward declarations for structures where possible. This
change reduces the build time for make M=drivers/target on my
laptop from 27.1s to 18.7s or by about 30%.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Bryant G. Ly <bryantly@linux.vnet.ibm.com>

include/target/iscsi/iscsi_target_core.h

@@ -1,12 +1,14 @@
 #ifndef ISCSI_TARGET_CORE_H
 #define ISCSI_TARGET_CORE_H
 
-#include <linux/in.h>
-#include <linux/configfs.h>
-#include <net/sock.h>
-#include <net/tcp.h>
-#include <scsi/iscsi_proto.h>
-#include <target/target_core_base.h>
+#include <linux/dma-direction.h>     /* enum dma_data_direction */
+#include <linux/list.h>              /* struct list_head */
+#include <linux/socket.h>            /* struct sockaddr_storage */
+#include <linux/types.h>             /* u8 */
+#include <scsi/iscsi_proto.h>        /* itt_t */
+#include <target/target_core_base.h> /* struct se_cmd */
+
+struct sock;
 
 #define ISCSIT_VERSION			"v4.1.0"
 #define ISCSI_MAX_DATASN_MISSING_COUNT	16

include/target/iscsi/iscsi_target_stat.h

@@ -1,6 +1,10 @@
 #ifndef ISCSI_TARGET_STAT_H
 #define ISCSI_TARGET_STAT_H
 
+#include <linux/types.h>
+#include <linux/spinlock.h>
+#include <linux/socket.h>
+
 /*
  * For struct iscsi_tiqn->tiqn_wwn default groups
  */

include/target/iscsi/iscsi_transport.h

@@ -1,6 +1,6 @@
-#include <linux/module.h>
-#include <linux/list.h>
-#include "iscsi_target_core.h"
+#include "iscsi_target_core.h" /* struct iscsi_cmd */
+
+struct sockaddr_storage;
 
 struct iscsit_transport {
 #define ISCSIT_TRANSPORT_NAME	16

include/target/target_core_backend.h

@@ -1,8 +1,14 @@
 #ifndef TARGET_CORE_BACKEND_H
 #define TARGET_CORE_BACKEND_H
 
+#include <linux/types.h>
+#include <target/target_core_base.h>
+
 #define TRANSPORT_FLAG_PASSTHROUGH		1
 
+struct request_queue;
+struct scatterlist;
+
 struct target_backend_ops {
 	char name[16];
 	char inquiry_prod[16];

include/target/target_core_base.h

@@ -1,14 +1,10 @@
 #ifndef TARGET_CORE_BASE_H
 #define TARGET_CORE_BASE_H
 
-#include <linux/in.h>
-#include <linux/configfs.h>
-#include <linux/dma-mapping.h>
-#include <linux/blkdev.h>
-#include <linux/percpu_ida.h>
-#include <linux/t10-pi.h>
-#include <net/sock.h>
-#include <net/tcp.h>
+#include <linux/configfs.h>      /* struct config_group */
+#include <linux/dma-direction.h> /* enum dma_data_direction */
+#include <linux/percpu_ida.h>    /* struct percpu_ida */
+#include <linux/semaphore.h>     /* struct semaphore */
 
 #define TARGET_CORE_VERSION		"v5.0"
 

include/target/target_core_fabric.h

@@ -1,6 +1,10 @@
 #ifndef TARGET_CORE_FABRIC_H
 #define TARGET_CORE_FABRIC_H
 
+#include <linux/configfs.h>
+#include <linux/types.h>
+#include <target/target_core_base.h>
+
 struct target_core_fabric_ops {
 	struct module *module;
 	const char *name;