Am 24.05.2016 um 13:48 hat Richard W.M. Jones geschrieben: > On Tue, May 17, 2016 at 03:35:09PM +0800, Fam Zheng wrote: > > v5: - Change "lock-image=on/off" to "lock-mode=exclusive/shared/off". > > Default is "lock-mode=exclusive" to exclusively lock RW images and > > shared > > lock RO images; with lock-mode="shared", RW images are shared locked > > too; > > lock-mode=off turns off image locking completely. > > - Use F_OFD_SETLK fcntl so that close/dup on different fds are not a > > problem. > > - Update test cases. > > My comments after testing this patch set: > > * It's not possible to tell from the `qemu -help' output that this > binary supports the lock-mode option. Please add this to the -help > output (under `-drive') so we can detect it in qemu. > > * I patched libguestfs to add the `lock-image=off' flag when the drive > is added readonly. This permits libguestfs to read live guests. I > also checked that writing to live guests is now forbidden, and it > is, which is good. In the write-to-live-guest case libguestfs will > now fail with: > > qemu-system-x86_64: -drive > file=/var/tmp/centos-6.img,cache=writeback,id=hd0,if=none: Failed to lock > image > > So definitely we need this option to be reflected in the -help output.
While you are right that maybe we should mentioned the new options in -help for human users, help texts are not meant to be parsed. If you do parse them and a changed help text breaks your code in the future, that's your problem. Consider using query-qmp-schema instead, that one is actually meant to be processed by machines. Kevin
