Add timeout for nfs mount within kdumpctl & mkdumprd

[liutgnu]

In kdumpctl and mkdumprd, for nfs dump target, cmd mount will be used to mount nfs dump target to local directory. However there is no time limit for mount, and it may take a long time for mount to finish, no matter success or fail, when network connection is unstable.

E.g we can emulate the package loss using the following command:

$ tc qdisc add dev tun0 root handle 1: prio
$ tc qdisc add dev tun0 parent 1:3 handle 30: netem delay 2000ms 1000ms loss 80%
$ tc filter add dev tun0 protocol ip parent 1:0 prio 3 u32 match ip dst <nfs_server_ip> flowid 1:3

This will emulate 80% network package loss to <nfs_server_ip>, then we invoke nfs mount:

$ time mount -t nfs <nfs_server_ip>:<nfs_dir> /mnt

real	354m56.200s
user	0m0.003s
sys		0m0.013s

$ mount | grep nfs
<nfs_server_ip>:<nfs_dir> on /mnt type nfs4 (...)

As we can see, though mount succeeded finally, it took near 6h to finish. The long time waiting makes no sense and should be ended as early, so user can check network issues and retry.

This issue also noticed in QE testing, because for beaker test tasks, if one task doesn't finish within a specific time period, the task will be killed and fail. We'd better set a timeout limit for nfs mount, in order to prevent it from connecting to nfs server timelessly.

This patch will set timeout duration as 5min for kdumpctl, and 10min for mkdumprd, as I think they are enough for normal cases as well as bail out as early if network do encounter problems.

[gemini-code-assist]

Summary of Changes

Hello @liutgnu, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces crucial timeout mechanisms for Network File System (NFS) mount operations within the kdumpctl and mkdumprd utilities. Previously, unstable network conditions could cause these mounts to hang for extended periods, impacting system reliability and test execution. The new timeouts ensure that NFS mount attempts fail gracefully within a defined timeframe, allowing for quicker diagnosis of network problems and improving overall system resilience.

Highlights

• NFS Mount Timeout in kdumpctl: Implemented a 5-minute timeout for NFS mount operations within the kdumpctl script to prevent indefinite hangs during network instability.
• NFS Mount Timeout in mkdumprd: Introduced a 10-minute timeout for NFS mount operations in mkdumprd to ensure timely failure and user feedback when network issues occur.
• Improved NFS Error Message: Enhanced the error message for NFS mount failures in mkdumprd to explicitly suggest checking NFS server accessibility, providing clearer guidance to users.

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[gemini-code-assist]

Code Review

This pull request introduces a timeout for NFS mount operations in kdumpctl and mkdumprd to prevent indefinite hangs during network instability. The changes are well-implemented and address the issue described. The updated error message in mkdumprd is also a helpful addition. I have a couple of minor suggestions to initialize variables for improved code clarity and robustness.