From: Greg Kurz <groug@kaod.org>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: virtio-fs@redhat.com, qemu-devel@nongnu.org,
Miklos Szeredi <miklos@szeredi.hu>
Subject: Re: [Virtio-fs] [for-6.1 2/2] virtiofsd: Add support for FUSE_SYNCFS request
Date: Wed, 21 Apr 2021 09:44:23 +0200 [thread overview]
Message-ID: <20210421094423.59e105f5@bahia.lan> (raw)
In-Reply-To: <20210420185719.GD1529659@redhat.com>
On Tue, 20 Apr 2021 14:57:19 -0400
Vivek Goyal <vgoyal@redhat.com> wrote:
> On Mon, Apr 19, 2021 at 05:11:42PM +0200, Greg Kurz wrote:
> > Honor the expected behavior of syncfs() to synchronously flush all
> > data and metadata on linux systems. Like the ->sync_fs() superblock
> > operation in the linux kernel, FUSE_SYNCFS has a 'wait' argument that
> > tells whether the server should wait for outstanding I/Os to complete
> > before replying to the client. Anything virtiofsd can do to flush
> > the caches implies blocking syscalls, so nothing is done if waiting
> > isn't requested.
> >
> > 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@kaod.org>
> > ---
> > 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..2d0c47a7a60e 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->wait);
> > + } 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..b5ac42c31799 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 wait whether to wait for outstanding I/Os to complete
> > + */
> > + void (*syncfs)(fuse_req_t req, int wait);
> > };
> >
> > /**
> > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
> > index 1553d2ef454f..6b66f3208be0 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, int wait)
> > +{
> > + if (wait) {
> > + struct lo_data *lo = lo_data(req);
> > + int fd, ret;
> > +
> > + 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);
> > + /* syncfs() never fails on a valid fd */
>
> Where does this come from. man page says.
>
> syncfs() can fail for at least the following reason:
>
> EBADF fd is not a valid file descriptor.
>
> It says "can fail for at least the following reason". Its not ruling out
> failures due to other reasons?
>
> Also kernel implementation of syscall is as follows.
>
> SYSCALL_DEFINE1(syncfs, int, fd)
> {
> if (!f.file)
> return -EBADF;
> sb = f.file->f_path.dentry->d_sb;
>
> down_read(&sb->s_umount);
> ret = sync_filesystem(sb);
> up_read(&sb->s_umount);
>
> ret2 = errseq_check_and_advance(&sb->s_wb_err, &f.file->f_sb_err);
>
> fdput(f);
> return ret ? ret : ret2;
> }
>
> So it explicityly capture error code from sync_filesystem() and
> errseq_check_and_advance() and returns one of them.
>
You're right. I'll drop the assert() and propagate the
error code.
> > + assert(ret == 0);
> > +
> > + close(fd);
> > + }
> > +
> > + fuse_reply_err(req, 0);
>
> This probably could be better strucutred as.
>
>
> if (!wait)
> goto out;
>
> /* Rest of the logic to call syncfs() */
> out:
> fuse_reply_err(req, ret);
>
Will do.
> Vivek
>
Cheers,
--
Greg
> > +}
>
> > +
> > 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
> >
> > _______________________________________________
> > Virtio-fs mailing list
> > Virtio-fs@redhat.com
> > https://listman.redhat.com/mailman/listinfo/virtio-fs
>
prev parent reply other threads:[~2021-04-21 7:45 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-19 15:11 [for-6.1 0/2] virtiofsd: Add support for FUSE_SYNCFS request Greg Kurz
2021-04-19 15:11 ` [for-6.1 1/2] Update linux headers to 5.12-rc8 + FUSE_SYNCFS Greg Kurz
2021-04-19 15:11 ` [for-6.1 2/2] virtiofsd: Add support for FUSE_SYNCFS request Greg Kurz
2021-04-20 18:57 ` [Virtio-fs] " Vivek Goyal
2021-04-21 7:44 ` Greg Kurz [this message]
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