When saving config files we just overwrite old content of the file. In
case something fails during that process (e.g. disk gets full) we lose
both old and new content. This patch makes the process more robust by
writing the new content into a separate file and only if that succeeds
the original file is atomically replaced with the new one.
Add some simple wrappers around the fcntl() discretionary file
locking capability.
* src/util/util.c, src/util/util.h, src/libvirt_private.syms: Add
virFileLock and virFileUnlock APIs
O_DIRECT has stringent requirements. Rather than make lots of changes
at each site that wants to use O_DIRECT, it is easier to offload
the work through a helper process that mirrors the I/O between a
pipe and the actual direct fd, so that the other end of the pipe
no longer has to worry about constraints.
Plus, if the kernel ever gains better posix_fadvise support, then we
only have to touch a single file to let all callers benefit from a
more efficient way to avoid file system caching.
* src/util/virfile.h (virFileDirectFdFlag, virFileDirectFdNew)
(virFileDirectFdClose, virFileDirectFdFree): New prototypes.
* src/util/virdirect.c: Implement new wrapper object.
* src/libvirt_private.syms (virfile.h): Export new symbols.
* cfg.mk (useless_free_options): Add to list.
* po/POTFILES.in: Add new translations.
