[Xen-devel] [PATCH] Fix bootloader handling when bootloader exits too early or didn't return any data

[Michal Novotny <minovotn@xxxxxxxxxx>]

Hi,
this is the patch to fix empty string handling as the output value of 
the bootloader string or when the bootloader process exists too early. 
Without this patch applied the xend process has been stuck indefinitely 
on the read() function in the bootloader() function since it was waiting 
for the bootloader process to open the write end of the pipe but if the 
bootloader process is bogus (e.g. just a user shell script returning 
with no output and code 0) that doesn't open a FIFO file the read() call 
was stuck. Therefore this patch is opening the FIFO with O_NDELAY flag 
to make it non-blocking and it uses pipe() and creates a separate thread 
for the wait on bootloader process to exit and when bootloader has 
exited the select() intercepts the end of bootloader process and breaks 
the loop.
I tried it with the bogus bootloader that just returns with error code 0 
and also the bogus bootloader that sleeps for 10 seconds and then 
returns with error code 0. According to my testing when the bootloader 
process has finished and the output of the process is empty it fails 
with "bootloader didn't return any data" message which is the expected 
behaviour. This patch has also been tested with the various timeout 
values (incl. no timeout specified) for pyGrub and everything was 
working fine since it was failing *only* in the case both output from 
pyGrub was empty and the bootloader process was not running according 
the pid.
The check for bootloader running is implemented by opening a pipe and 
passing the write end of the pipe to the new thread
that's waiting for the bootloader process to be terminated. When it's 
terminated it's writing to the write end of the pipe
which is being read by the bootloader() method to terminate the loop.

Testing: The patch has been tested on RHEL-5.5 x86_64 dom0 with latest 
version of upstream Xen installed (staging) and RHEL-5.4 PV guest both 
with good and bad bootloader setup. By bad bootloader I mean just the 
shell script exiting with code 0 and also shell script sleeping for 10 
seconds and exiting with code 0. All the tests passed successfully when 
having following Ian's patch applied: libxl+xend: use correct paths for 
PV console when running bootloader
Signed-off-by: Michal Novotny <minovotn@xxxxxxxxxx>

Michal

Michal Novotny<minovotn@xxxxxxxxxx>, RHCE
Virtualization Team (xen userspace), Red Hat

Attachment: fix-bootloader-empty-output-handling.patch
Description: Text Data

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