[stgt] [PATCH] Make backends loadable modules

[Andy Grover]

On 08/20/2013 07:46 PM, Ronnie Sahlberg wrote:
> Tomo,
>
> Please find a second version of the patch to make the backing stores
> into loadable modules so that distributors can ship core tgtd as one
> package and individual backends as separate packages. This prevents
> having just a single module for everyone which depends on and
> requires a huge set of dependent packets.
>
> This is version 2 This version only changes bs.c into a shared
> library that the backend modules can link with at runtimie instead of
> as in the first patch changing all of tgtd into a shared library.
>
>
> regards ronnie sahlberg

Hi Ronnie,

I think you may be able to avoid making bs.c into a shared library if 
you link tgtd with the -E linker option.

I've attached a patch that Fedora tgt carried for a little while that 
modularized iser. I think my approach to iser modularization was bad and 
it got dropped, but you could loot it for some Makefile magic :)

Regards -- Andy
-------------- next part --------------
commit 1aa20610d4a3afc22e9a0b24efa4bbb7b02dfab2
Author: Andy Grover <agrover at redhat.com>
Date:   Wed Sep 28 11:21:38 2011 -0700

    Compile iser driver as a loadable module
    
    Drivers are already modularized in the code, so it is straightforward to
    change the build to target a separate loadable module. Also, modify
    get_driver_index to try to load a module when lld is unknown.
    
    This will allow packaging of base tgtd and iser module separately, so
    the majority of users will not have to install dependencies they don't
    need.
    
    Signed-off-by: Andy Grover <agrover at redhat.com>

diff --git a/usr/Makefile b/usr/Makefile
index e15ff6a..b8ab805 100644
--- a/usr/Makefile
+++ b/usr/Makefile
@@ -1,4 +1,5 @@
 sbindir ?= $(PREFIX)/sbin
+libdir ?= $(PREFIX)/lib/tgt
 
 ifneq ($(shell test -e /usr/include/linux/signalfd.h && echo 1),)
 CFLAGS += -DUSE_SIGNALFD
@@ -13,11 +14,6 @@ TGTD_OBJS += $(addprefix iscsi/, conn.o param.o session.o \
 		isns.o)
 TGTD_OBJS += bs_rdwr.o bs_aio.o
 
-ifneq ($(ISCSI_RDMA),)
-TGTD_OBJS += iscsi/iser.o iscsi/iser_text.o
-LIBS += -libverbs -lrdmacm
-endif
-
 INCLUDES += -I.
 
 CFLAGS += -D_GNU_SOURCE
@@ -30,9 +26,13 @@ endif
 CFLAGS += -Wall -Wstrict-prototypes -fPIC
 CFLAGS += -DTGT_VERSION=\"$(VERSION)$(EXTRAVERSION)\"
 
-LIBS += -lpthread
+LIBS += -lpthread -ldl
 
 PROGRAMS += tgtd tgtadm tgtimg
+ifneq ($(ISCSI_RDMA),)
+DRIVERS += tgt-iser.so
+endif
+
 TGTD_OBJS += tgtd.o mgmt.o target.o scsi.o log.o driver.o util.o work.o \
 		parser.o spc.o sbc.o mmc.o osd.o scc.o smc.o \
 		ssc.o bs_ssc.o libssc.o \
@@ -41,10 +41,12 @@ TGTD_OBJS += tgtd.o mgmt.o target.o scsi.o log.o driver.o util.o work.o \
 TGTD_DEP = $(TGTD_OBJS:.o=.d)
 
 .PHONY:all
-all: $(PROGRAMS)
+all: $(PROGRAMS) $(DRIVERS)
+
+LDFLAGS = -Wl,-E,-rpath=$(libdir)
 
 tgtd: $(TGTD_OBJS)
-	$(CC) $^ -o $@ $(LIBS)
+	$(CC) $^ -o $@ $(LDFLAGS) $(LIBS)
 
 -include $(TGTD_DEP)
 
@@ -58,15 +60,23 @@ tgtimg: tgtimg.o libssc.o libcrc32c.o
 
 -include tgtimg.d libssc.d
 
+tgt-iser.so: CFLAGS += -shared -libverbs -lrdmacm
+tgt-iser.so: iscsi/iser.o iscsi/iser_text.o
+	$(CC) $(CFLAGS) -o $@ $^
+
 %.o: %.c
 	$(CC) -c $(CFLAGS) $*.c -o $*.o
 	@$(CC) -MM $(CFLAGS) -MF $*.d -MT $*.o $*.c
 
 .PHONY: install
-install: $(PROGRAMS)
+install: $(PROGRAMS) $(DRIVERS)
 	install -d -m 755 $(DESTDIR)$(sbindir)
 	install -m 755 $(PROGRAMS) $(DESTDIR)$(sbindir)
+ifneq ($(DRIVERS),)
+	install -d -m 755 $(DESTDIR)$(libdir)
+	install -m 755 $(DRIVERS) $(DESTDIR)$(libdir)
+endif
 
 .PHONY: clean
 clean:
-	rm -f *.[od] $(PROGRAMS) iscsi/*.[od] ibmvio/*.[od] fc/*.[od]
+	rm -f *.[od] $(PROGRAMS) *.so iscsi/*.[od] ibmvio/*.[od] fc/*.[od]
diff --git a/usr/tgtd.c b/usr/tgtd.c
index 30d5e9d..a9b2027 100644
--- a/usr/tgtd.c
+++ b/usr/tgtd.c
@@ -35,6 +35,7 @@
 #include <sys/epoll.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <dlfcn.h>
 
 #include "list.h"
 #include "tgtd.h"
@@ -411,6 +412,9 @@ static int lld_init(char *args)
 {
 	int i, err, nr;
 
+	/* iser is modular, try to load it */
+	dlopen("tgt-iser.so", RTLD_LAZY);
+
 	for (i = nr = 0; tgt_drivers[i]; i++) {
 		if (tgt_drivers[i]->init) {
 			err = tgt_drivers[i]->init(i, args);