On Fri, Aug 21, 2020 at 7:58 PM Daniel P. Berrangé <berra...@redhat.com> wrote:
> On Fri, Aug 21, 2020 at 11:41:26AM +0800, Jiachen Zhang wrote: > > Due to the commit 65da4539803373ec4eec97ffc49ee90083e56efd, the O_DIRECT > > open flag of guest applications will be discarded by virtiofsd. While > > this behavior makes it consistent with the virtio-9p scheme when guest > > applications using direct I/O, we no longer have any chance to bypass > > the host page cache. > > > > Therefore, we add a flag 'allow_directio' to lo_data. If '-o no_directio' > > option is added, or none of '-o no_directio' or '-o allow_directio' is > > added, the 'allow_directio' will be set to 0, and virtiofsd discards > > O_DIRECT as before. If '-o allow_directio' is added to the stariting > > command-line, 'allow_directio' will be set to 1, so that the O_DIRECT > > flags will be retained and host page cache can be bypassed. > > > > Signed-off-by: Jiachen Zhang <zhangjiachen.jay...@bytedance.com> > > --- > > tools/virtiofsd/helper.c | 4 ++++ > > tools/virtiofsd/passthrough_ll.c | 20 ++++++++++++++------ > > 2 files changed, 18 insertions(+), 6 deletions(-) > > > > diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c > > index 3105b6c23a..534ff52c64 100644 > > --- a/tools/virtiofsd/helper.c > > +++ b/tools/virtiofsd/helper.c > > @@ -180,6 +180,10 @@ void fuse_cmdline_help(void) > > " (0 leaves rlimit > unchanged)\n" > > " default: min(1000000, > fs.file-max - 16384)\n" > > " if the current > rlimit is lower\n" > > + " -o allow_directio|no_directio\n" > > + " retain/discard O_DIRECT > flags passed down\n" > > + " to virtiofsd from guest > applications.\n" > > + " default: no_directio\n" > > ); > > The standard naming convention from existing options is to use > $OPTNAME and no_$OPTNAME. > > IOW, don't use the "allow_" prefix. The options should be just > "directio" and "no_directio" > > Thanks, Daniel. I did consider using "directio" instead of "allow_directio" before I send out this patch. Although "-o directio" makes it consistent with other option names, it may confuse the users of virtiofsd. Because currently, virtiofsd will not add an O_DIRECT to the open flag, it will just retain or discard the O_DIRECT added by guest applications. But "-o direct" may make the users think that virtiofsd will do direct IO all the time. Jiachen > > Regards, > Daniel > -- > |: https://berrange.com -o- > https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- > https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- > https://www.instagram.com/dberrange :| >
