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,
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.
Just mentioning it here so that we have a note about the limitation of
current patch.
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
>
