On Wed, 5 May 2021 14:52:42 -0400
Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> On Mon, Apr 26, 2021 at 05:21:35PM +0200, Greg Kurz wrote:
> > Honor the expected behavior of syncfs() to synchronously flush all
> > data and metadata on linux systems.
> >
> > Flushing is done with syncfs(). This is suboptimal as it will also
> > flush writes performed by any other process on the same file system,
> > and thus add an unbounded time penalty to syncfs(). This may be
> > optimized in the future, but enforce correctness first.
> >
> > Signed-off-by: Greg Kurz <groug@xxxxxxxx>
> > ---
> > tools/virtiofsd/fuse_lowlevel.c | 19 ++++++++++++++++++
> > tools/virtiofsd/fuse_lowlevel.h | 13 ++++++++++++
> > tools/virtiofsd/passthrough_ll.c | 29 +++++++++++++++++++++++++++
> > tools/virtiofsd/passthrough_seccomp.c | 1 +
> > 4 files changed, 62 insertions(+)
> >
> > diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c
> > index 58e32fc96369..918ab11f54c2 100644
> > --- a/tools/virtiofsd/fuse_lowlevel.c
> > +++ b/tools/virtiofsd/fuse_lowlevel.c
> > @@ -1870,6 +1870,24 @@ static void do_lseek(fuse_req_t req, fuse_ino_t nodeid,
> > }
> > }
> >
> > +static void do_syncfs(fuse_req_t req, fuse_ino_t nodeid,
> > + struct fuse_mbuf_iter *iter)
> > +{
> > + struct fuse_syncfs_in *arg;
> > +
> > + arg = fuse_mbuf_iter_advance(iter, sizeof(*arg));
> > + if (!arg) {
> > + fuse_reply_err(req, EINVAL);
> > + return;
> > + }
> > +
> > + if (req->se->op.syncfs) {
> > + req->se->op.syncfs(req, arg->flags);
> > + } else {
> > + fuse_reply_err(req, ENOSYS);
> > + }
> > +}
> > +
> > static void do_init(fuse_req_t req, fuse_ino_t nodeid,
> > struct fuse_mbuf_iter *iter)
> > {
> > @@ -2267,6 +2285,7 @@ static struct {
> > [FUSE_RENAME2] = { do_rename2, "RENAME2" },
> > [FUSE_COPY_FILE_RANGE] = { do_copy_file_range, "COPY_FILE_RANGE" },
> > [FUSE_LSEEK] = { do_lseek, "LSEEK" },
> > + [FUSE_SYNCFS] = { do_syncfs, "SYNCFS" },
> > };
> >
> > #define FUSE_MAXOP (sizeof(fuse_ll_ops) / sizeof(fuse_ll_ops[0]))
> > diff --git a/tools/virtiofsd/fuse_lowlevel.h b/tools/virtiofsd/fuse_lowlevel.h
> > index 3bf786b03485..220bb3db4898 100644
> > --- a/tools/virtiofsd/fuse_lowlevel.h
> > +++ b/tools/virtiofsd/fuse_lowlevel.h
> > @@ -1225,6 +1225,19 @@ struct fuse_lowlevel_ops {
> > */
> > void (*lseek)(fuse_req_t req, fuse_ino_t ino, off_t off, int whence,
> > struct fuse_file_info *fi);
> > +
> > + /**
> > + * Synchronize file system content
> > + *
> > + * If this request is answered with an error code of ENOSYS,
> > + * this is treated as success and future calls to syncfs() will
> > + * succeed automatically without being sent to the filesystem
> > + * process.
> > + *
> > + * @param req request handle
> > + * @param flags not used yet
> > + */
> > + void (*syncfs)(fuse_req_t req, uint64_t flags);
> > };
> >
> > /**
> > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
> > index 1553d2ef454f..6790a2f6fe10 100644
> > --- a/tools/virtiofsd/passthrough_ll.c
> > +++ b/tools/virtiofsd/passthrough_ll.c
> > @@ -3124,6 +3124,34 @@ static void lo_lseek(fuse_req_t req, fuse_ino_t ino, off_t off, int whence,
> > }
> > }
> >
> > +static void lo_syncfs(fuse_req_t req, uint64_t flags)
> > +{
> > + struct lo_data *lo = lo_data(req);
> > + int fd, ret;
> > +
> > + /* No flags supported yet */
> > + if (flags) {
> > + fuse_reply_err(req, EINVAL);
> > + return;
> > + }
> > +
> > + fd = lo_inode_open(lo, &lo->root, O_RDONLY);
> > + if (fd < 0) {
> > + fuse_reply_err(req, errno);
> > + return;
> > + }
> > +
> > + /*
> > + * FIXME: this is suboptimal because it will also flush unrelated
> > + * writes not coming from the client. This can dramatically
> > + * increase the time spent in syncfs() if some process is
> > + * writing lots of data on the same filesystem as virtiofsd.
> > + */
> > + ret = syncfs(fd);
>
> Hi Greg,
>
Hi Vivek,
> As we discussed in the community call that this works only if there are
> no other filesystems mounted as submounts under exported directory.
>
> We proably need to find a way to call syncfs() on all the filesystems
> which are submounts of exported directory. Might not be easy at all.
>
I must confess I didn't investigate this case. I'll start looking.
> Just mentioning it here so that we have a note about the limitation of
> current patch.
>
Sure. I'll add a note for that.
> Vivek
>
> > + fuse_reply_err(req, ret < 0 ? errno : 0);
> > + close(fd);
> > +}
> > +
> > static void lo_destroy(void *userdata)
> > {
> > struct lo_data *lo = (struct lo_data *)userdata;
> > @@ -3184,6 +3212,7 @@ static struct fuse_lowlevel_ops lo_oper = {
> > .copy_file_range = lo_copy_file_range,
> > #endif
> > .lseek = lo_lseek,
> > + .syncfs = lo_syncfs,
> > .destroy = lo_destroy,
> > };
> >
> > diff --git a/tools/virtiofsd/passthrough_seccomp.c b/tools/virtiofsd/passthrough_seccomp.c
> > index 62441cfcdb95..343188447901 100644
> > --- a/tools/virtiofsd/passthrough_seccomp.c
> > +++ b/tools/virtiofsd/passthrough_seccomp.c
> > @@ -107,6 +107,7 @@ static const int syscall_allowlist[] = {
> > SCMP_SYS(set_robust_list),
> > SCMP_SYS(setxattr),
> > SCMP_SYS(symlinkat),
> > + SCMP_SYS(syncfs),
> > SCMP_SYS(time), /* Rarely needed, except on static builds */
> > SCMP_SYS(tgkill),
> > SCMP_SYS(unlinkat),
> > --
> > 2.26.3
> >
>
