[Qemu-block] [PATCH 1/2] block/file-posix: Fix fully preallocated truncate

[Max Reitz]

Storing the lseek() result in an int results in it overflowing when the
file is at least 2 GB big.  Then, we have a 50 % chance of the result
being "negative" and thus thinking an error occurred when actually
everything went just fine.

So we should use the correct type for storing the result: off_t.

Reported-by: Daniel P. Berrange <address@hidden>
Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1549231
Cc: address@hidden
Signed-off-by: Max Reitz <address@hidden>
---
 block/file-posix.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index f1591c3849..90c25864a0 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1697,6 +1697,7 @@ static int raw_regular_truncate(int fd, int64_t offset, 
PreallocMode prealloc,
     case PREALLOC_MODE_FULL:
     {
         int64_t num = 0, left = offset - current_length;
+        off_t seek_result;
 
         /*
          * Knowing the final size from the beginning could allow the file
@@ -1711,8 +1712,8 @@ static int raw_regular_truncate(int fd, int64_t offset, 
PreallocMode prealloc,
 
         buf = g_malloc0(65536);
 
-        result = lseek(fd, current_length, SEEK_SET);
-        if (result < 0) {
+        seek_result = lseek(fd, current_length, SEEK_SET);
+        if (seek_result < 0) {
             result = -errno;
             error_setg_errno(errp, -result,
                              "Failed to seek to the old end of file");
-- 
2.14.3