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

On 4/12/22 7:23 PM, Ani Sinha wrote: > On Tue, Apr 12, 2022 at 10:09 PM Ani Sinha <ani(a)anisinha.ca&gt; wrote: > >> On Tue, Apr 12, 2022 at 2:48 PM Claudio Fontana <cfontana(a)suse.de&gt; 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; >>> + } >> >> There is an obvious issue with this code. We are trying to close and >> free a file descriptor that we have not opened when >> VIR_DOMAIN_SAVE_BYPASS_CACHE is set in flags. > > > I meant *not* set in flags. I don't think so. I don't think it is obvious, so can you be more specific?

From the function header comments it seems lecit and defined to call the function with NULL: /** * virFileWrapperFdClose: * @wfd: fd wrapper, or NULL * * If @wfd is valid, then ensure that I/O has completed, which may * include reaping a child process. Return 0 if all data for the * wrapped fd is complete, or -1 on failure with an error emitted. * This function intentionally returns 0 when @wfd is NULL, so that * callers can conditionally create a virFileWrapperFd wrapper but * unconditionally call the cleanup code. To avoid deadlock, only * call this after closing the fd resulting from virFileWrapperFdNew(). * * This function can be safely called multiple times on the same @wfd. */ Seems it has been specifically designed to simplify situations like this. Thanks, Claudio > > >> >>> >>> if (virQEMUSaveDataWrite(data, fd, path) < 0) >>> goto cleanup; >>> -- >>> 2.34.1 >>> >> >