I can change to doing this if it preferred,
Simon
________________________________
From: Michal Prívozník <mprivozn(a)redhat.com>
Sent: 20 August 2021 16:09
To: Simon Rowe <simon.rowe(a)nutanix.com>; libvir-list(a)redhat.com
<libvir-list(a)redhat.com>
Subject: Re: [PATCH 1/2] iohelper: skip lseek() and ftruncate() on block devices
On 8/20/21 10:39 AM, Simon Rowe wrote:
Signed-off-by: Simon Rowe <simon.rowe(a)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;
}
IIUC, O_DIRECT is no good for block devices. I wonder whether the caller
(doCoreDump()) should learn whether the path is a block device and don't
set O_DIRECT flag instead of changing iohelper.
Michal