[stgt] [PATCH] Add support for modular backends

[FUJITA Tomonori]

On Thu, 19 Sep 2013 16:30:41 -0700
Ronnie Sahlberg <ronniesahlberg at gmail.com> wrote:

> Link tgtd with -E so all symbols are available for runtime linking
> by dynamically loaded objects.
> Build some modules, such as bs_{aio|ssc|rdwr|rbd} as shared objects and
> install them under /usr/lib/tgtd/backing-store
> Add support so that when tgtd is started and initializes the backends
> it will traverse /usr/lib/tgtd/backing-store and dynamically load
> all object files.

s/tgtd/tgt/ ?

> This allows to build and distribute backends as separate packages than tgtd.
> TGTD can be shipped with only base dependencies and basic backend support
> and then those backends that include extra dependencies can be shipped
> and installed separately.
> 
> Signed-off-by: Ronnie Sahlberg <ronniesahlberg at gmail.com>
> ---
>  usr/Makefile |   35 ++++++++++++++++++++++++-----------
>  usr/bs.c     |   52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  usr/bs_aio.c |    2 +-
>  usr/bs_rbd.c |    2 +-
>  4 files changed, 78 insertions(+), 13 deletions(-)
> 
> diff --git a/usr/Makefile b/usr/Makefile
> index 453eb1a..35f11fd 100644
> --- a/usr/Makefile
> +++ b/usr/Makefile
> @@ -1,4 +1,5 @@
>  sbindir ?= $(PREFIX)/sbin
> +libdir ?= $(PREFIX)/lib/tgtd
>  
>  ifneq ($(shell test -e /usr/include/linux/signalfd.h && echo 1),)
>  CFLAGS += -DUSE_SIGNALFD
> @@ -11,17 +12,14 @@ endif
>  TGTD_OBJS += $(addprefix iscsi/, conn.o param.o session.o \
>  		iscsid.o target.o chap.o sha1.o md5.o transport.o iscsi_tcp.o \
>  		isns.o)
> -TGTD_OBJS += bs_rdwr.o
>  
>  ifneq ($(CEPH_RBD),)
> -TGTD_OBJS += bs_rbd.o
> -LIBS += -lrados -lrbd
> +MODULES += bs_rbd.so
>  endif
>  
>  ifneq ($(shell test -e /usr/include/sys/eventfd.h && test -e /usr/include/libaio.h && echo 1),)
>  CFLAGS += -DUSE_EVENTFD
> -TGTD_OBJS += bs_aio.o
> -LIBS += -laio
> +MODULES += bs_aio.o
>  endif
>  
>  ifneq ($(ISCSI_RDMA),)
> @@ -40,22 +38,26 @@ CFLAGS += -g -O2 -fno-strict-aliasing
>  endif
>  CFLAGS += -Wall -Wstrict-prototypes -fPIC
>  CFLAGS += -DTGT_VERSION=\"$(VERSION)$(EXTRAVERSION)\"
> +CFLAGS += -DBSDIR=\"$(DESTDIR)$(libdir)/backing-store\"
>  
> -LIBS += -lpthread
> +LIBS += -lpthread -ldl
>  
>  PROGRAMS += tgtd tgtadm tgtimg
>  TGTD_OBJS += tgtd.o mgmt.o target.o scsi.o log.o driver.o util.o work.o \
>  		concat_buf.o parser.o spc.o sbc.o mmc.o osd.o scc.o smc.o \
> -		ssc.o bs_ssc.o libssc.o \
> +		ssc.o libssc.o bs_rdwr.o bs_ssc.o \
>  		bs_null.o bs_sg.o bs.o libcrc32c.o
>  
>  TGTD_DEP = $(TGTD_OBJS:.o=.d)
>  
> +LDFLAGS = -Wl,-E,-rpath=$(libdir)
> +
>  .PHONY:all
> -all: $(PROGRAMS)
> +all: $(PROGRAMS) $(MODULES)
>  
>  tgtd: $(TGTD_OBJS)
> -	$(CC) $^ -o $@ $(LIBS)
> +	echo $(CC) $^ -o $@ $(LIBS)
> +	$(CC) $^ -o $@ $(LDFLAGS) $(LIBS)
>  
>  -include $(TGTD_DEP)
>  
> @@ -79,11 +81,22 @@ tgtimg: $(TGTIMG_OBJS)
>  	$(CC) -c $(CFLAGS) $*.c -o $*.o
>  	@$(CC) -MM $(CFLAGS) -MF $*.d -MT $*.o $*.c
>  
> +%.so: %.c
> +	$(CC) -shared $(CFLAGS) $*.c -o $*.so
> +
> +bs_aio.so: bs_aio.c
> +	$(CC) -shared $(CFLAGS) bs_aio.c -o bs_aio.so -laio
> +
> +bs_rbd.so: bs_rbd.c
> +	$(CC) -shared $(CFLAGS) bs_rbd.c -o bs_rbd.so -lrados -lrbd
> +
>  .PHONY: install
> -install: $(PROGRAMS)
> +install: $(PROGRAMS) $(MODULES)
>  	install -d -m 755 $(DESTDIR)$(sbindir)
>  	install -m 755 $(PROGRAMS) $(DESTDIR)$(sbindir)
> +	install -d -m 755 $(DESTDIR)$(libdir)/backing-store
> +	install -m 755 $(MODULES) $(DESTDIR)$(libdir)/backing-store
>  
>  .PHONY: clean
>  clean:
> -	rm -f *.[od] $(PROGRAMS) iscsi/*.[od] ibmvio/*.[od] fc/*.[od]
> +	rm -f *.[od] *.so $(PROGRAMS) iscsi/*.[od] ibmvio/*.[od] fc/*.[od]
> diff --git a/usr/bs.c b/usr/bs.c
> index 65c332e..739ab81 100644
> --- a/usr/bs.c
> +++ b/usr/bs.c
> @@ -19,6 +19,12 @@
>   * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
>   * 02110-1301 USA
>   */
> +#define _GNU_SOURCE
> +#include <dirent.h>
> +#include <dlfcn.h>
> +#include <linux/fs.h>
> +#include <sys/ioctl.h>
> +#include <stdio.h>
>  #include <errno.h>
>  #include <string.h>
>  #include <inttypes.h>
> @@ -31,7 +37,9 @@
>  #include <syscall.h>
>  #include <sys/types.h>
>  #include <sys/epoll.h>
> +#include <sys/stat.h>
>  #include <linux/types.h>
> +#include <unistd.h>
>  
>  #include "list.h"
>  #include "tgtd.h"
> @@ -233,6 +241,50 @@ static int bs_init_signalfd(void)
>  {
>  	sigset_t mask;
>  	int ret;
> +	DIR *dir;
> +
> +	dir = opendir(BSDIR);
> +	if (dir == NULL) {
> +		eprintf("could not open backing-store module directory %s\n",
> +			BSDIR); 
> +	} else {
> +		struct dirent *dirent;
> +		void *handle;
> +		while ((dirent = readdir(dir))) {
> +			char *soname;
> +			void (*register_bs_module)(void);
> +
> +			if (dirent->d_name[0] == '.') {
> +				continue;
> +			}
> +
> +			ret = asprintf(&soname, "%s/%s", BSDIR,
> +					dirent->d_name);
> +			if (ret == -1) {
> +				eprintf("out of memory\n");
> +				continue;
> +			}
> +			handle = dlopen(soname, RTLD_NOW|RTLD_LOCAL);
> +			if (handle == NULL) {
> +				eprintf("failed to dlopen backing-store "
> +					"module %s error %s \n",
> +					soname, dlerror());
> +				free(soname);
> +				continue;
> +			}
> +			register_bs_module = dlsym(handle, "register_bs_module");
> +			if (register_bs_module == NULL) {
> +				eprintf("could not find register_bs_module "
> +					"symbol in module %s\n",
> +					soname);
> +				free(soname);
> +				continue;
> +			}
> +			register_bs_module();
> +			free(soname);
> +		}
> +		closedir(dir);
> +	}
>  
>  	pthread_mutex_init(&finished_lock, NULL);
>  
> diff --git a/usr/bs_aio.c b/usr/bs_aio.c
> index c0cbadd..cc59cf6 100644
> --- a/usr/bs_aio.c
> +++ b/usr/bs_aio.c
> @@ -414,7 +414,7 @@ static struct backingstore_template aio_bst = {
>  	.bs_cmd_submit  	= bs_aio_cmd_submit,
>  };
>  
> -__attribute__((constructor)) static void bs_rdwr_constructor(void)
> +void register_bs_module(void)
>  {
>  	register_backingstore_template(&aio_bst);
>  }
> diff --git a/usr/bs_rbd.c b/usr/bs_rbd.c
> index b09090b..f1dd77d 100644
> --- a/usr/bs_rbd.c
> +++ b/usr/bs_rbd.c
> @@ -529,7 +529,7 @@ static struct backingstore_template rbd_bst = {
>  	.bs_oflags_supported    = O_SYNC | O_DIRECT,
>  };
>  
> -static __attribute__((constructor)) void bs_rbd_constructor(void)
> +void register_bs_module(void)
>  {
>  	register_backingstore_template(&rbd_bst);
>  }
> -- 
> 1.7.3.1
> 
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