[libvirt] [PATCH v2 3/3] virstoragefile: Refactor virStorageFileResize

[John Ferlan]

Currently virStorageFileResize() function uses build conditionals to
choose either the posix_fallocate() or mmap() with no fallback in order
to preallocate the space in the newly resized file.

This patch will modify the logic in order to allow fallbacks in the event
that posix_fallocate() or the sys_fallocate syscall() doesn't work properly.
The fallback will be to use the slow safewrite of zero filled buffers to
the file.

Use the virFileFdPosixFallocate() rather than a local function.

Signed-off-by: John Ferlan <jferlan at redhat.com>
---
 src/util/virstoragefile.c | 52 +++++++++++++++++++++++++++++++----------------
 1 file changed, 34 insertions(+), 18 deletions(-)

diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c
index 5b6b2f5..4d37de1 100644
--- a/src/util/virstoragefile.c
+++ b/src/util/virstoragefile.c
@@ -1086,6 +1086,39 @@ virStorageFileChainGetBroken(virStorageSourcePtr chain,
     return 0;
 }
 
+static int
+resizeSysFallocate(const char *path,
+                   int fd,
+                   off_t offset,
+                   off_t len)
+{
+    int rc = -1;
+#if HAVE_SYS_SYSCALL_H && defined(SYS_fallocate)
+    if ((rc = syscall(SYS_fallocate, fd, 0, offset, len)) != 0) {
+        virReportSystemError(errno,
+                             _("Failed to pre-allocate space for "
+                             "file '%s'"), path);
+    }
+#endif
+    return rc;
+}
+
+static int
+doResize(const char *path,
+         int fd,
+         off_t offset,
+         off_t len)
+{
+    if (virFileFdPosixFallocate(fd, offset, len) == 0 ||
+        resizeSysFallocate(path, fd, offset, len) == 0 ||
+        safezero(fd, offset, len) == 0)
+        return 0;
+
+    virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
+                   _("preallocate is not supported on this platform"));
+    return -1;
+}
+
 
 /**
  * virStorageFileResize:
@@ -1113,25 +1146,8 @@ virStorageFileResize(const char *path,
     }
 
     if (pre_allocate) {
-#if HAVE_POSIX_FALLOCATE
-        if ((rc = posix_fallocate(fd, offset, len)) != 0) {
-            virReportSystemError(rc,
-                                 _("Failed to pre-allocate space for "
-                                   "file '%s'"), path);
-            goto cleanup;
-        }
-#elif HAVE_SYS_SYSCALL_H && defined(SYS_fallocate)
-        if (syscall(SYS_fallocate, fd, 0, offset, len) != 0) {
-            virReportSystemError(errno,
-                                 _("Failed to pre-allocate space for "
-                                   "file '%s'"), path);
+        if (doResize(path, fd, offset, len) < 0)
             goto cleanup;
-        }
-#else
-        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
-                       _("preallocate is not supported on this platform"));
-        goto cleanup;
-#endif
     } else {
         if (ftruncate(fd, capacity) < 0) {
             virReportSystemError(errno,
-- 
1.9.3