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Re: [PATCH v6 1/1] virtiofsd: Add basic support for FUSE_SYNCFS request
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [PATCH v6 1/1] virtiofsd: Add basic support for FUSE_SYNCFS request |
Date: |
Wed, 16 Feb 2022 12:18:13 +0000 |
User-agent: |
Mutt/2.1.5 (2021-12-30) |
* Vivek Goyal (vgoyal@redhat.com) wrote:
> On Tue, Feb 15, 2022 at 07:15:29PM +0100, Greg Kurz wrote:
> > Honor the expected behavior of syncfs() to synchronously flush all data
> > and metadata to disk on linux systems.
> >
> > If virtiofsd is started with '-o announce_submounts', the client is
> > expected to send a FUSE_SYNCFS request for each individual submount.
> > In this case, we just create a new file descriptor on the submount
> > inode with lo_inode_open(), call syncfs() on it and close it. The
> > intermediary file is needed because O_PATH descriptors aren't
> > backed by an actual file and syncfs() would fail with EBADF.
> >
> > If virtiofsd is started without '-o announce_submounts' or if the
> > client doesn't have the FUSE_CAP_SUBMOUNTS capability, the client
> > only sends a single FUSE_SYNCFS request for the root inode. The
> > server would thus need to track submounts internally and call
> > syncfs() on each of them. This will be implemented later.
> >
> > Note that syncfs() might suffer from a time penalty if the submounts
> > are being hammered by some unrelated workload on the host. The only
> > solution to prevent that is to avoid shared mounts.
> >
> > Signed-off-by: Greg Kurz <groug@kaod.org>
>
> Looks good to me. Thanks Greg.
>
> Reviewed-by: Vivek Goyal <vgoyal@redhat.com>
Queued
> Vivek
>
> > ---
> > tools/virtiofsd/fuse_lowlevel.c | 11 +++++++
> > tools/virtiofsd/fuse_lowlevel.h | 13 ++++++++
> > tools/virtiofsd/passthrough_ll.c | 44 +++++++++++++++++++++++++++
> > tools/virtiofsd/passthrough_seccomp.c | 1 +
> > 4 files changed, 69 insertions(+)
> >
> > diff --git a/tools/virtiofsd/fuse_lowlevel.c
> > b/tools/virtiofsd/fuse_lowlevel.c
> > index e4679c73abc2..e02d8b25a5f6 100644
> > --- a/tools/virtiofsd/fuse_lowlevel.c
> > +++ b/tools/virtiofsd/fuse_lowlevel.c
> > @@ -1876,6 +1876,16 @@ 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)
> > +{
> > + if (req->se->op.syncfs) {
> > + req->se->op.syncfs(req, nodeid);
> > + } else {
> > + fuse_reply_err(req, ENOSYS);
> > + }
> > +}
> > +
> > static void do_init(fuse_req_t req, fuse_ino_t nodeid,
> > struct fuse_mbuf_iter *iter)
> > {
> > @@ -2280,6 +2290,7 @@ 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 c55c0ca2fc1c..b889dae4de0e 100644
> > --- a/tools/virtiofsd/fuse_lowlevel.h
> > +++ b/tools/virtiofsd/fuse_lowlevel.h
> > @@ -1226,6 +1226,19 @@ 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 ino the inode number
> > + */
> > + void (*syncfs)(fuse_req_t req, fuse_ino_t ino);
> > };
> >
> > /**
> > diff --git a/tools/virtiofsd/passthrough_ll.c
> > b/tools/virtiofsd/passthrough_ll.c
> > index b3d0674f6d2f..0f65e6423cf5 100644
> > --- a/tools/virtiofsd/passthrough_ll.c
> > +++ b/tools/virtiofsd/passthrough_ll.c
> > @@ -3357,6 +3357,49 @@ static void lo_lseek(fuse_req_t req, fuse_ino_t ino,
> > off_t off, int whence,
> > }
> > }
> >
> > +static int lo_do_syncfs(struct lo_data *lo, struct lo_inode *inode)
> > +{
> > + int fd, ret = 0;
> > +
> > + fuse_log(FUSE_LOG_DEBUG, "lo_do_syncfs(ino=%" PRIu64 ")\n",
> > + inode->fuse_ino);
> > +
> > + fd = lo_inode_open(lo, inode, O_RDONLY);
> > + if (fd < 0) {
> > + return -fd;
> > + }
> > +
> > + if (syncfs(fd) < 0) {
> > + ret = errno;
> > + }
> > +
> > + close(fd);
> > + return ret;
> > +}
> > +
> > +static void lo_syncfs(fuse_req_t req, fuse_ino_t ino)
> > +{
> > + struct lo_data *lo = lo_data(req);
> > + struct lo_inode *inode = lo_inode(req, ino);
> > + int err;
> > +
> > + if (!inode) {
> > + fuse_reply_err(req, EBADF);
> > + return;
> > + }
> > +
> > + err = lo_do_syncfs(lo, inode);
> > + lo_inode_put(lo, &inode);
> > +
> > + /*
> > + * If submounts aren't announced, the client only sends a request to
> > + * sync the root inode. TODO: Track submounts internally and iterate
> > + * over them as well.
> > + */
> > +
> > + fuse_reply_err(req, err);
> > +}
> > +
> > static void lo_destroy(void *userdata)
> > {
> > struct lo_data *lo = (struct lo_data *)userdata;
> > @@ -3417,6 +3460,7 @@ 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 a3ce9f898d2d..3e9d6181dc69 100644
> > --- a/tools/virtiofsd/passthrough_seccomp.c
> > +++ b/tools/virtiofsd/passthrough_seccomp.c
> > @@ -108,6 +108,7 @@ 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),
> > --
> > 2.34.1
> >
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK