On Tue, 2017-06-20 at 17:03 +0200, Erik Skultety wrote:
Since we have a number of places where we workaround timing issues
with
devices, attributes (files in general) not being available at the
time
of processing them by calling usleep in a loop for a fixed number of
tries, we could as well have a utility function that would do that.
Therefore we won't have to duplicate this ugly workaround even more.
This is a prerequisite for
https://bugzilla.redhat.com/show_bug.cgi?id=1463285.
Signed-off-by: Erik Skultety <eskultet(a)redhat.com>
---
src/libvirt_private.syms | 1 +
src/util/virfile.c | 36 ++++++++++++++++++++++++++++++++++++
src/util/virfile.h | 2 ++
3 files changed, 39 insertions(+)
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index c1e9471c5..53878a30f 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1698,6 +1698,7 @@ virFileStripSuffix;
virFileTouch;
virFileUnlock;
virFileUpdatePerm;
+virFileWaitForAccess;
virFileWrapperFdClose;
virFileWrapperFdFree;
virFileWrapperFdNew;
diff --git a/src/util/virfile.c b/src/util/virfile.c
index 6bbcc3d15..0b1a91699 100644
--- a/src/util/virfile.c
+++ b/src/util/virfile.c
@@ -4164,3 +4164,39 @@ virFileReadValueString(char **value, const
char *format, ...)
VIR_FREE(str);
return ret;
}
+
+
+/**
+ * virFileWaitForAccess:
+ * @path: absolute path to a sysfs attribute (can be a symlink)
+ * @ms: how long to wait (in milliseconds)
+ * @tries: how many times should we try to wait for @path to become
accessible
+ *
+ * Checks the existence of @path. In case the file defined by @path
+ * doesn't exist, we wait for it to appear in 100ms (for up to
@tries times).
+ *
+ * Returns 0 on success, -1 on error (ENOENT is fine here).
+ */
+int
+virFileWaitForAccess(const char *path, size_t ms, size_t tries)
+{
+ errno = 0;
+
+ /* wait for @path to be accessible in @ms milliseconds, up to
@tries */
+ while (tries-- > 0 && !virFileExists(path)) {
+ if (errno != ENOENT) {
+ virReportSystemError(errno, "%s", path);
+ return -1;
+ } else if (tries == 10) {
+ virReportError(VIR_ERR_INTERNAL_ERROR,
+ _("Failed to access '%s' after %zu
tries"),
+ path, tries);
+ return -1;
+ } else {
+ VIR_DEBUG("Failed to access '%s', re-try in %zu ms",
path, ms);
+ usleep(ms * 1000);
+ }
+ }
+
+ return 0;
+}
Just FYI, there's another way to address it by calling udevadm settle
before and after "touching" a block device, libguestfs is using this
approach and it works very well:
https://github.com/libguestfs/libguestfs/search?utf8=%E2%9C%93&q=udev_s
ettle&type=
diff --git a/src/util/virfile.h b/src/util/virfile.h
index 57ceb8072..42630ebb5 100644
--- a/src/util/virfile.h
+++ b/src/util/virfile.h
@@ -347,6 +347,8 @@ int virFileReadValueScaledInt(unsigned long long
*value, const char *format, ...
int virFileReadValueString(char **value, const char *format, ...)
ATTRIBUTE_FMT_PRINTF(2, 3);
+int virFileWaitForAccess(const char *path, size_t ms, size_t tries);
+
int virFileInData(int fd,
int *inData,