Re: [libvirt] [PATCH 3/4] Cache result of QEMU capabilities extraction

Extracting capabilities from QEMU takes a notable amount of time when all QEMU binaries are installed. Each system emulator needs about 200-300ms multiplied by 26 binaries == ~5-8 seconds. This change causes the QEMU driver to save an XML file containing the content of the virQEMUCaps object instance in the cache dir eg /var/cache/libvirt/qemu/capabilities/$SHA256(binarypath).xml or $HOME/.cache/libvirt/qemu/cache/capabilities/$SHA256(binarypath).xml We attempt to load this and only if it fails, do we fallback to probing the QEMU binary. The timestamp of the file is compared to the timestamp of the QEMU binary and discarded if the QEMU binary is newer. Signed-off-by: Daniel P. Berrange <berrange(a)redhat.com&gt; --- src/qemu/qemu_capabilities.c | 412 ++++++++++++++++++++++++++++++++++++++++++- src/qemu/qemu_capabilities.h | 2 + src/qemu/qemu_driver.c | 1 + 3 files changed, 407 insertions(+), 8 deletions(-)

@@ -44,6 +45,7 @@ #include <unistd.h> #include <sys/wait.h> #include <stdarg.h> +#include <utime.h>

+ + ut.actime = qemuCaps->mtime; + ut.modtime = qemuCaps->mtime; + if (utime(filename, &ut) < 0) { + virReportSystemError(errno, + _("Failed to set mtime on '%s' for '%s'"), + filename, qemuCaps->binary);

+ + /* Discard if cache is older that QEMU binary */ + /* XXX must also compare to libvirtd timestamp */ + if (sb.st_mtime < qemuCaps->mtime) {