[PATCH v2 04/20] fuse: Allow growable exports

[Max Reitz <mreitz@redhat.com>]

These will behave more like normal files in that writes beyond the EOF
will automatically grow the export size.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 qapi/block-export.json |  6 +++++-
 block/export/fuse.c    | 12 +++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/qapi/block-export.json b/qapi/block-export.json
index cb5bd54cbf..cb26daa98b 100644
--- a/qapi/block-export.json
+++ b/qapi/block-export.json
@@ -183,10 +183,14 @@
 # @mountpoint: Path on which to export the block device via FUSE.
 #              This must point to an existing regular file.
 #
+# @growable: Whether writes beyond the EOF should grow the block node
+#            accordingly. (default: false)
+#
 # Since: 5.2
 ##
 { 'struct': 'BlockExportOptionsFuse',
-  'data': { 'mountpoint': 'str' },
+  'data': { 'mountpoint': 'str',
+            '*growable': 'bool' },
   'if': 'defined(CONFIG_FUSE)' }
 
 ##
diff --git a/block/export/fuse.c b/block/export/fuse.c
index 8fc667231d..f3a84579ba 100644
--- a/block/export/fuse.c
+++ b/block/export/fuse.c
@@ -45,6 +45,7 @@ typedef struct FuseExport {
 
     char *mountpoint;
     bool writable;
+    bool growable;
 } FuseExport;
 
 static GHashTable *exports;
@@ -101,6 +102,7 @@ static int fuse_export_create(BlockExport *blk_exp,
 
     exp->mountpoint = g_strdup(args->mountpoint);
     exp->writable = blk_exp_args->writable;
+    exp->growable = args->growable;
 
     ret = setup_fuse_export(exp, args->mountpoint, errp);
     if (ret < 0) {
@@ -436,7 +438,15 @@ static void fuse_write(fuse_req_t req, fuse_ino_t inode, const char *buf,
 
     size = MIN(size, BDRV_REQUEST_MAX_BYTES);
     if (offset + size > length) {
-        size = length - offset;
+        if (exp->growable) {
+            ret = fuse_do_truncate(exp, offset + size, PREALLOC_MODE_OFF);
+            if (ret < 0) {
+                fuse_reply_err(req, -ret);
+                return;
+            }
+        } else {
+            size = length - offset;
+        }
     }
 
     ret = blk_pwrite(exp->common.blk, offset, buf, size, 0);
-- 
2.26.2