qsd: Document FUSE exports
Implementing FUSE exports required no changes to the storage daemon, so
we forgot to document them there. Considering that both NBD and
vhost-user-blk exports are documented in its man page (and NBD exports
in its --help text), we should probably do the same for FUSE.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20210217115844.62661-1-mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/docs/tools/qemu-storage-daemon.rst b/docs/tools/qemu-storage-daemon.rst
index 086493e..3ec4bdd 100644
--- a/docs/tools/qemu-storage-daemon.rst
+++ b/docs/tools/qemu-storage-daemon.rst
@@ -74,6 +74,7 @@
.. option:: --export [type=]nbd,id=<id>,node-name=<node-name>[,name=<export-name>][,writable=on|off][,bitmap=<name>]
--export [type=]vhost-user-blk,id=<id>,node-name=<node-name>,addr.type=unix,addr.path=<socket-path>[,writable=on|off][,logical-block-size=<block-size>][,num-queues=<num-queues>]
--export [type=]vhost-user-blk,id=<id>,node-name=<node-name>,addr.type=fd,addr.str=<fd>[,writable=on|off][,logical-block-size=<block-size>][,num-queues=<num-queues>]
+ --export [type=]fuse,id=<id>,node-name=<node-name>,mountpoint=<file>[,growable=on|off][,writable=on|off]
is a block export definition. ``node-name`` is the block node that should be
exported. ``writable`` determines whether or not the export allows write
@@ -92,6 +93,16 @@
``logical-block-size`` sets the logical block size in bytes (the default is
512). ``num-queues`` sets the number of virtqueues (the default is 1).
+ The ``fuse`` export type takes a mount point, which must be a regular file,
+ on which to export the given block node. That file will not be changed, it
+ will just appear to have the block node's content while the export is active
+ (very much like mounting a filesystem on a directory does not change what the
+ directory contains, it only shows a different content while the filesystem is
+ mounted). Consequently, applications that have opened the given file before
+ the export became active will continue to see its original content. If
+ ``growable`` is set, writes after the end of the exported file will grow the
+ block node to fit.
+
.. option:: --monitor MONITORDEF
is a QMP monitor definition. See the :manpage:`qemu(1)` manual page for
@@ -196,6 +207,14 @@
--blockdev driver=qcow2,node-name=qcow2,file=file \
--export type=vhost-user-blk,id=export,addr.type=unix,addr.path=vhost-user-blk.sock,node-name=qcow2
+Export a qcow2 image file ``disk.qcow2`` via FUSE on itself, so the disk image
+file will then appear as a raw image::
+
+ $ qemu-storage-daemon \
+ --blockdev driver=file,node-name=file,filename=disk.qcow2 \
+ --blockdev driver=qcow2,node-name=qcow2,file=file \
+ --export type=fuse,id=export,node-name=qcow2,mountpoint=disk.qcow2,writable=on
+
See also
--------
diff --git a/storage-daemon/qemu-storage-daemon.c b/storage-daemon/qemu-storage-daemon.c
index 72900dc..fc8b150 100644
--- a/storage-daemon/qemu-storage-daemon.c
+++ b/storage-daemon/qemu-storage-daemon.c
@@ -98,6 +98,10 @@
" export the specified block node over NBD\n"
" (requires --nbd-server)\n"
"\n"
+" --export [type=]fuse,id=<id>,node-name=<node-name>,mountpoint=<file>\n"
+" [,growable=on|off][,writable=on|off]\n"
+" export the specified block node over FUSE\n"
+"\n"
" --monitor [chardev=]name[,mode=control][,pretty[=on|off]]\n"
" configure a QMP monitor\n"
"\n"
