docs: add qemu-block-drivers(7) man page

Block driver documentation is available in qemu-doc.html.  It would be
convenient to have documentation for formats, protocols, and filter
drivers in a man page.

Extract the relevant part of qemu-doc.html into a new file called
docs/qemu-block-drivers.texi.  This file can also be built as a
stand-alone document (man, html, etc).
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

Makefile

@@ -209,6 +209,7 @@ ifdef BUILD_DOCS
 DOCS=qemu-doc.html qemu-doc.txt qemu.1 qemu-img.1 qemu-nbd.8 qemu-ga.8
 DOCS+=docs/interop/qemu-qmp-ref.html docs/interop/qemu-qmp-ref.txt docs/interop/qemu-qmp-ref.7
 DOCS+=docs/interop/qemu-ga-ref.html docs/interop/qemu-ga-ref.txt docs/interop/qemu-ga-ref.7
+DOCS+=docs/qemu-block-drivers.7
 ifdef CONFIG_VIRTFS
 DOCS+=fsdev/virtfs-proxy-helper.1
 endif
@@ -532,6 +533,7 @@ distclean: clean
 	rm -f docs/interop/qemu-qmp-ref.txt docs/interop/qemu-ga-ref.txt
 	rm -f docs/interop/qemu-qmp-ref.pdf docs/interop/qemu-ga-ref.pdf
 	rm -f docs/interop/qemu-qmp-ref.html docs/interop/qemu-ga-ref.html
+	rm -f docs/qemu-block-drivers.7
 	for d in $(TARGET_DIRS); do \
 	rm -rf $$d || exit 1 ; \
         done
@@ -576,6 +578,7 @@ ifdef CONFIG_POSIX
 	$(INSTALL_DATA) qemu.1 "$(DESTDIR)$(mandir)/man1"
 	$(INSTALL_DIR) "$(DESTDIR)$(mandir)/man7"
 	$(INSTALL_DATA) docs/interop/qemu-qmp-ref.7 "$(DESTDIR)$(mandir)/man7"
+	$(INSTALL_DATA) docs/qemu-block-drivers.7 "$(DESTDIR)$(mandir)/man7"
 ifneq ($(TOOLS),)
 	$(INSTALL_DATA) qemu-img.1 "$(DESTDIR)$(mandir)/man1"
 	$(INSTALL_DIR) "$(DESTDIR)$(mandir)/man8"
@@ -721,6 +724,7 @@ qemu-img.1: qemu-img.texi qemu-option-trace.texi qemu-img-cmds.texi
 fsdev/virtfs-proxy-helper.1: fsdev/virtfs-proxy-helper.texi
 qemu-nbd.8: qemu-nbd.texi qemu-option-trace.texi
 qemu-ga.8: qemu-ga.texi
+docs/qemu-block-drivers.7: docs/qemu-block-drivers.texi
 
 html: qemu-doc.html docs/interop/qemu-qmp-ref.html docs/interop/qemu-ga-ref.html
 info: qemu-doc.info docs/interop/qemu-qmp-ref.info docs/interop/qemu-ga-ref.info
@@ -730,7 +734,7 @@ txt: qemu-doc.txt docs/interop/qemu-qmp-ref.txt docs/interop/qemu-ga-ref.txt
 qemu-doc.html qemu-doc.info qemu-doc.pdf qemu-doc.txt: \
 	qemu-img.texi qemu-nbd.texi qemu-options.texi qemu-option-trace.texi \
 	qemu-monitor.texi qemu-img-cmds.texi qemu-ga.texi \
-	qemu-monitor-info.texi
+	qemu-monitor-info.texi docs/qemu-block-drivers.texi
 
 docs/interop/qemu-ga-ref.dvi docs/interop/qemu-ga-ref.html \
     docs/interop/qemu-ga-ref.info docs/interop/qemu-ga-ref.pdf \