Re: [libvirt RFC] qemu_saveimage: only use wrapper when using --bypass-cache

On Tue, Apr 12, 2022 at 11:18:15AM +0200, Claudio Fontana wrote: > align the "save" with the "restore" code, > by only using the wrapper when using --bypass-cache. > > This avoids a copy, resulting in better performance. > > Signed-off-by: Claudio Fontana <cfontana(a)suse.de&gt; > --- > src/qemu/qemu_saveimage.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/src/qemu/qemu_saveimage.c b/src/qemu/qemu_saveimage.c > index 4fd4c5cfcd..5ea1b2fbcc 100644 > --- a/src/qemu/qemu_saveimage.c > +++ b/src/qemu/qemu_saveimage.c > @@ -289,8 +289,10 @@ qemuSaveImageCreate(virQEMUDriver *driver, > if (qemuSecuritySetImageFDLabel(driver->securityManager, vm->def, fd) < 0) > goto cleanup; > > - if (!(wrapperFd = virFileWrapperFdNew(&fd, path, wrapperFlags))) > - goto cleanup; > + if ((flags & VIR_DOMAIN_SAVE_BYPASS_CACHE)) { > + if (!(wrapperFd = virFileWrapperFdNew(&fd, path, wrapperFlags))) > + goto cleanup; > + } This effectively reverts: commit c4caab538effb57411ad787fedb61e80d557caae Author: Jiri Denemark <jdenemar(a)redhat.com&gt; Date: Wed Feb 8 14:08:54 2012 +0100 qemu: Always use iohelper for domain save This is probably not strictly needed as save operation is not live but we may have other reasons to avoid blocking qemu's main loop. As the commit message mentions, using a plain file FD results in the QEMU thread being blocked, even when O_NONBLOCK is used.