[PATCHv2 1/2] iohelper: skip lseek() and ftruncate() on block devices

[Simon Rowe]

Signed-off-by: Simon Rowe <simon.r...@nutanix.com>
---
 src/util/iohelper.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/util/iohelper.c b/src/util/iohelper.c
index b8810d16d3..e6eb178fde 100644
--- a/src/util/iohelper.c
+++ b/src/util/iohelper.c
@@ -28,6 +28,8 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
 
 #include "virthread.h"
 #include "virfile.h"
@@ -56,6 +58,8 @@ runIO(const char *path, int fd, int oflags)
     unsigned long long total = 0;
     bool direct = O_DIRECT && ((oflags & O_DIRECT) != 0);
     off_t end = 0;
+    struct stat sb;
+    bool isBlockDev = false;
 
 #if WITH_POSIX_MEMALIGN
     if (posix_memalign(&base, alignMask + 1, buflen))
@@ -86,9 +90,11 @@ runIO(const char *path, int fd, int oflags)
         fdinname = "stdin";
         fdout = fd;
         fdoutname = path;
+        if (fstat(fd, &sb) == 0)
+            isBlockDev = S_ISBLK(sb.st_mode);
         /* To make the implementation simpler, we give up on any
          * attempt to use O_DIRECT in a non-trivial manner.  */
-        if (direct && (end = lseek(fd, 0, SEEK_END)) != 0) {
+        if (!isBlockDev && direct && (end = lseek(fd, 0, SEEK_END)) != 0) {
             virReportSystemError(end < 0 ? errno : EINVAL, "%s",
                                  _("O_DIRECT write needs empty seekable 
file"));
             goto cleanup;
@@ -140,7 +146,7 @@ runIO(const char *path, int fd, int oflags)
                 goto cleanup;
             }
 
-            if (ftruncate(fd, total) < 0) {
+            if (!isBlockDev && ftruncate(fd, total) < 0) {
                 virReportSystemError(errno, _("Unable to truncate %s"), 
fdoutname);
                 goto cleanup;
             }
-- 
2.22.3