[PATCH 1/2] iohelper: skip lseek() and ftruncate() on block devices
Simon Rowe
simon.rowe at nutanix.com
Fri Aug 20 15:59:53 UTC 2021
I can change to doing this if it preferred,
Simon
________________________________
From: Michal Prívozník <mprivozn at redhat.com>
Sent: 20 August 2021 16:09
To: Simon Rowe <simon.rowe at nutanix.com>; libvir-list at redhat.com <libvir-list at 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 at 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
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