In some scenarios (e.g. apexd or userspace reboot), dm-devices are
getting deleted and re-created. Since this operation can be racy (newly
created device can get the same path as the previously deleted one,
resulting in the unexpected ENOENT errors on a system call to the path),
it will be nice to have an API that blocks until ueventd processes
corresponding udev events.
Test: libdm_test
Bug: 143970043
Bug: 122059364
Change-Id: I31a19afd9e245bf5e3554011bdde1c3cc4878f1c
This fixes two race conditions in LoopControl::Attach(). The first is
that after LOOP_CTL_GET_FREE, the path is not be available until it has
been processed by ueventd. This can be fixed by adding a timeout
parameter and a call to WaitForFile().
Second, it is possible (albeit unlikely), given that loop devices are
now being used more aggressively, that two processes race when
attempting LOOP_SET_FD. In this case, one process will win, and the
other will fail with EBUSY. We can handle this case by retrying the
operation while respecting the same timeout parameter.
Bug: 135771280
Test: libdm_test gtest
Change-Id: Icf9facc3ca28fdb6ff5c78612d3dc183fa47b1f3
Nikita Ioffe
David Anderson