commit b4542c5594d0028bb8a6fc3975f7000d45d291f5
author James Tucker <raggi@google.com> Thu Mar 15 14:47:21 2018 -0700
committer CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org> Fri Mar 16 22:55:12 2018 +0000
tree b3cd1f07f65c1e60f8ce62254b20b5728588261d
parent ee1b65d893625d73920630bfdc37726f1cd4d60f

[fvm] create images with specified length

It is sometimes useful to be able to specify the size that an FVM image
should be on the command line. The length flag can be used for this
purpose, the file just needs to be truncated to that size.

Change-Id: I9ce00b2c32858d56b6789e24649d393274f3f19a

system/host/fvm/main.cpp

diff --git a/system/host/fvm/main.cpp b/system/host/fvm/main.cpp
index 7e3ab22..163664b 100644
--- a/system/host/fvm/main.cpp
+++ b/system/host/fvm/main.cpp
@@ -4,6 +4,7 @@
 
 #include <fbl/alloc_checker.h>
 #include <fbl/unique_ptr.h>
+#include <unistd.h>
 
 #include "fvm/container.h"
 
@@ -112,6 +113,17 @@
     }
 
     if (!strcmp(command, "create")) {
+
+        // If length was specified, an offset was not, we were asked to create a
+        // file, and the file does not exist, truncate it to the given length.
+        if (length != 0 && offset == 0) {
+            fbl::unique_fd fd(open(path, O_CREAT|O_EXCL|O_WRONLY, 0644));
+
+            if (fd) {
+                ftruncate(fd.get(), length);
+            }
+        }
+
         fbl::unique_ptr<FvmContainer> fvmContainer;
         if (FvmContainer::Create(path, slice_size, offset, length, &fvmContainer) != ZX_OK) {
             return -1;