.

wcfs/internal/wcfs_misc.cpp

@@ -19,6 +19,7 @@
 
 #include "wcfs_misc.h"
 
+// os::
 namespace os {
 
 tuple<File, error> open(const string &path) {
@@ -51,5 +52,25 @@ error File::_err(const char *op) {
     return errorf("%s %s: %s", op, f->path, strerror_r(errno));
 }
 
-
 }   // os::
+
+
+// fmt::
+namespace fmt {
+
+string sprintf(const string &format, ...) {
+    // https://stackoverflow.com/a/26221725/9456786
+    va_list ap;
+
+    va_start(ap, format);
+    size_t size = vsnprintf(NULL, 0, format.c_str(), ap);
+    va_end(ap);
+
+    std::unique_ptr<char[]> buf( new char[size] );
+    va_start(ap, format);
+    vsnprintf(buf.get(), size, format.c_str(), ap);
+    va_end(ap);
+    return string(buf.get(), buf.get() + size - 1 ); // without trailing '\0'
+}
+
+}   // fmt::

wcfs/internal/wcfs_misc.h

@@ -27,6 +27,7 @@ using std::string;
 
 #include <tuple>
 using std::tuple;
+using std::tie;
 
 // nil is synonim for nullptr and NULL.
 const nullptr_t nil = nullptr;
@@ -45,6 +46,7 @@ struct error {
     }
 };
 
+// os::
 namespace os {
 
 // os::File mimics os.File from Go.
@@ -63,4 +65,12 @@ tuple<File, error> open(const string &path);
 
 }   // os::
 
+
+// fmt::
+namespace fmt {
+
+string sprintf(const string &format, ...);
+
+}   // fmt::
+
 #endif

wcfs/internal/wcfs_virtmem.cpp

@@ -240,6 +240,7 @@ error _Mapping::_remmapblk(int64_t blk, Tid at) {
 
     ASSERT(mmap->blk_start <= blk && blk < mmap->blk_stop());
     _File *f = mmap->file;
+    error err;
 
     uint8_t *blkmem = mmap->mem_start + (blk - mmap->blk_start)*f->blksize;
     os::File fsfile;
@@ -248,13 +249,15 @@ error _Mapping::_remmapblk(int64_t blk, Tid at) {
     }
     else {
         // TODO share @rev fd until wconn is resynced?
-        fsfile = f->wconn->_wc->_open("@%s/bigfile/%s" % (h(at), h(f->foid)), "rb");
-        // XXX err
+        tie(fsfile, err) = f->wconn->_wc->_open(
+                fmt::sprintf("@%s/bigfile/%s", h(at), h(f->foid), "rb");
+        if (err != nil)
+            return err;
         defer(fsfile.close);
     }
 
     struct stat st;
-    auto err = fsfile.stat(&st);
+    err = fsfile.stat(&st);
     if (err != nil)
         return err;
     ASSERT(st.st_blksize == f->blksize);  // FIXME assert