MythTV and network mounts

After setting up a MythTv 0.24 frontend to use a samba share for files from the backend I discovered that I could no longer watch live TV on it. If I tried to watch live TV there would just be a pause and then a "Error opening jump program file buffer" error message. Looking in the output on stdout wasn't much more helpful, with "Error: Took more than 10 seconds to be allowed to read, aborting" being about the only meaningful message.

It took me ages to track down that the problem is with cached IO on the network share. If the CIFS file system is caching the inode information (which includes the size attributes), then the MythTv frontend thinks that no live TV is being streamed and gives up after a while.

The solution to this is to add the 'directio' option when mounting the network partition (e.g. '-o directio' on the command line). If it's an NFS share then an alternative is to use 'forcedirectio' in the /etc/exports on the server (which is useful if you don't want to change all your MythTv frontends).