On Tue, 20 Apr 2021 14:57:19 -0400 Vivek Goyal <vgo...@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 <gr...@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...@redhat.com > > https://listman.redhat.com/mailman/listinfo/virtio-fs >