[Libguestfs] [PATCH 3/3] daemon: Run udev_settle after pwrite-device finishes.

[Richard W.M. Jones]

From: "Richard W.M. Jones" <rjones at redhat.com>

When you call close on any block device, udev kicks off a rule which
runs blkid to reexamine the device.  We need to wait for this rule to
finish running since it holds the device open and can cause other
operations to fail, notably BLKRRPART.
---
 daemon/file.c   |   17 ++++++++++++++---
 daemon/parted.c |    3 ++-
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/daemon/file.c b/daemon/file.c
index 91746e0..3e42c1e 100644
--- a/daemon/file.c
+++ b/daemon/file.c
@@ -525,7 +525,7 @@ do_pread_device (const char *device, int count, int64_t offset, size_t *size_r)
 
 static int
 pwrite_fd (int fd, const char *content, size_t size, int64_t offset,
-           const char *display_path)
+           const char *display_path, int settle)
 {
   ssize_t r;
 
@@ -541,6 +541,17 @@ pwrite_fd (int fd, const char *content, size_t size, int64_t offset,
     return -1;
   }
 
+  /* When you call close on any block device, udev kicks off a rule
+   * which runs blkid to reexamine the device.  We need to wait for
+   * this rule to finish running since it holds the device open and
+   * can cause other operations to fail, notably BLKRRPART.
+   *
+   * XXX We should be smarter about when we do this or should get rid
+   * of the udev rules since we don't use blkid in cached mode.
+   */
+  if (settle)
+    udev_settle ();
+
   return r;
 }
 
@@ -563,7 +574,7 @@ do_pwrite (const char *path, const char *content, size_t size, int64_t offset)
     return -1;
   }
 
-  return pwrite_fd (fd, content, size, offset, path);
+  return pwrite_fd (fd, content, size, offset, path, 0);
 }
 
 int
@@ -581,7 +592,7 @@ do_pwrite_device (const char *device, const char *content, size_t size,
     return -1;
   }
 
-  return pwrite_fd (fd, content, size, offset, device);
+  return pwrite_fd (fd, content, size, offset, device, 1);
 }
 
 /* This runs the 'file' command. */
diff --git a/daemon/parted.c b/daemon/parted.c
index 16f0843..64a7d1d 100644
--- a/daemon/parted.c
+++ b/daemon/parted.c
@@ -34,7 +34,8 @@
  * COMMAND_FLAG_FOLD_STDOUT_ON_STDERR flag.
  *
  * parted occasionally fails to do ioctl(BLKRRPART) on the device,
- * apparently because of some internal race in the code.  We attempt
+ * probably because udev monitors all 'close' on block devices
+ * and runs 'blkid' which opens and examines the device.  We attempt
  * to detect and recover from this error if we can.
  */
 static int
-- 
1.7.6