I can change to doing this if it preferred, Simon ________________________________ From: Michal Prívozník <mprivozn@redhat.com> Sent: 20 August 2021 16:09 To: Simon Rowe <simon.rowe@nutanix.com>; libvir-list@redhat.com <libvir-list@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@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