Re: [External] Re: [RFC PATCH 6/9] virtiofsd: Add two new options for crash reconnection

[Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>]

[-- Attachment #1: Type: text/plain, Size: 12224 bytes --]

On Thu, Feb 4, 2021 at 8:09 PM Dr. David Alan Gilbert <dgilbert@redhat.com>
wrote:

> * Jiachen Zhang (zhangjiachen.jaycee@bytedance.com) wrote:
> > We add two options for virtiofsd crash reconnection: reconnect |
> > no_reconnect(default) and
> >
> > User of virtiofsd should set "-o reconnect" for crash reconnection. Note
> > that, when "-o reconnect" is set, some options will not be supported and
> we
> > need to disable them:
> >
> >   - mount namespace: When mount namespace is enabled, reconnected
> >     virtiofsd will failed to link/rename for EXDEV. The reason is, when
> >     virtiofsd is sandboxed by mount namespace, attempts to link/rename
> >     the fds opened before crashing (also recovered from QEMU) will be
> >     considered as across mount operations between mounts, which is not
> >     allowed by host kernel.
> >
> >     So we introduce another option "-o mount_ns|no_mount_ns" (mount_ns
> >     by default, and takes no effect when sandbox=chroot is specified).
> >     The option "-o no_mount_ns" should be used with "-o reconnect".
>
> Why not just use -o sandbox=chroot?
>
>
Yes, thanks. I think this is a good idea, and maybe better than add the new
options
(mount_ns | no_mount_ns). Actually, "-o sandbox=" has not been upstream
when we
add the new options.


> >   - remote locking: As it is hard to determine wether a file is locked or
> >     not when handling inflight locking requests, we should specify "-o
> >     no_posix_lock" (default) and "-o no_flock" (default).
> >
> >   - extended attributes: When handling inflight removexattr requests
> after
> >     reconnecting, it is hard to determine wether a attr is already
> removed
> >     or not. Therefore, we should also use "-o noxattr" (default) with "-o
> >     reconnect".
>
> Can you explain a bit more about why removexattr is hard to restart?
>
>
Consider the following removexattr handling procedure:

    lo_removexattr() {
        (1) // ......
        (2). fremovexattr / removexattr
        (3) // ......
        (4). fuse_reply_err(req, saverr);
    }

If virtiofsd successfully executed (2) but crashes at (3). When new
virtiofsd is
reconnected, as (4) is not executed before crashing, this fuse request will
be
re-executed from (1), and (2) will be executed for the second time. As the
xattr
is already removed by the first execution of (2), this time an ENODATA will
be
returned by (2) and mistakenly replied to fuse by (4).

Jiachen


> Dave
> >
> > Signed-off-by: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>
> > Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> > ---
> >  tools/virtiofsd/helper.c         |   9 +++
> >  tools/virtiofsd/passthrough_ll.c | 112 ++++++++++++++++++++++---------
> >  2 files changed, 88 insertions(+), 33 deletions(-)
> >
> > diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c
> > index 75ac48dec2..e0d6525b1a 100644
> > --- a/tools/virtiofsd/helper.c
> > +++ b/tools/virtiofsd/helper.c
> > @@ -174,6 +174,10 @@ void fuse_cmdline_help(void)
> >             "                               - chroot: chroot(2) into
> shared\n"
> >             "                                 directory (use in
> containers)\n"
> >             "                               default: namespace\n"
> > +           "    -o mount_ns|no_mount_ns    enable/disable mount
> namespace\n"
> > +           "                               default: mount_ns\n"
> > +           "                               note: if chroot sandbox mode
> is used,\n"
> > +           "                               mount_ns will not take
> effect.\n"
> >             "    -o timeout=<number>        I/O timeout (seconds)\n"
> >             "                               default: depends on cache=
> option.\n"
> >             "    -o writeback|no_writeback  enable/disable writeback
> cache\n"
> > @@ -191,6 +195,11 @@ void fuse_cmdline_help(void)
> >             "                               to virtiofsd from guest
> applications.\n"
> >             "                               default:
> no_allow_direct_io\n"
> >             "    -o announce_submounts      Announce sub-mount points to
> the guest\n"
> > +           "    -o reconnect|no_reconnect  enable/disable crash
> reconnection\n"
> > +           "                               to enable crash
> reconnection, the options\n"
> > +           "                               no_mount_ns, no_flock,
> no_posix_lock, and\n"
> > +           "                               no_xattr should also be
> set.\n"
> > +           "                               default: no_reconnect\n"
> >             );
> >  }
> >
> > diff --git a/tools/virtiofsd/passthrough_ll.c
> b/tools/virtiofsd/passthrough_ll.c
> > index 815b001076..73a50bd7a3 100644
> > --- a/tools/virtiofsd/passthrough_ll.c
> > +++ b/tools/virtiofsd/passthrough_ll.c
> > @@ -170,6 +170,8 @@ struct lo_data {
> >      pthread_mutex_t mutex;
> >      int sandbox;
> >      int debug;
> > +    int mount_ns;
> > +    int reconnect;
> >      int writeback;
> >      int flock;
> >      int posix_lock;
> > @@ -204,8 +206,12 @@ static const struct fuse_opt lo_opts[] = {
> >      { "sandbox=chroot",
> >        offsetof(struct lo_data, sandbox),
> >        SANDBOX_CHROOT },
> > +    { "reconnect", offsetof(struct lo_data, reconnect), 1 },
> > +    { "no_reconnect", offsetof(struct lo_data, reconnect), 0 },
> >      { "writeback", offsetof(struct lo_data, writeback), 1 },
> >      { "no_writeback", offsetof(struct lo_data, writeback), 0 },
> > +    { "mount_ns", offsetof(struct lo_data, mount_ns), 1 },
> > +    { "no_mount_ns", offsetof(struct lo_data, mount_ns), 0 },
> >      { "source=%s", offsetof(struct lo_data, source), 0 },
> >      { "flock", offsetof(struct lo_data, flock), 1 },
> >      { "no_flock", offsetof(struct lo_data, flock), 0 },
> > @@ -3047,8 +3053,14 @@ static void setup_namespaces(struct lo_data *lo,
> struct fuse_session *se)
> >       * an empty network namespace to prevent TCP/IP and other network
> >       * activity in case this process is compromised.
> >       */
> > -    if (unshare(CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWNET) != 0) {
> > -        fuse_log(FUSE_LOG_ERR, "unshare(CLONE_NEWPID | CLONE_NEWNS):
> %m\n");
> > +    int unshare_flag;
> > +    if (lo->mount_ns) {
> > +        unshare_flag = CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWNET;
> > +    } else {
> > +        unshare_flag = CLONE_NEWPID | CLONE_NEWNET;
> > +    }
> > +    if (unshare(unshare_flag) != 0) {
> > +        fuse_log(FUSE_LOG_ERR, "unshare(): %m\n");
> >          exit(1);
> >      }
> >
> > @@ -3083,38 +3095,47 @@ static void setup_namespaces(struct lo_data *lo,
> struct fuse_session *se)
> >      /* Send us SIGTERM when the parent thread terminates, see prctl(2)
> */
> >      prctl(PR_SET_PDEATHSIG, SIGTERM);
> >
> > -    /*
> > -     * If the mounts have shared propagation then we want to opt out so
> our
> > -     * mount changes don't affect the parent mount namespace.
> > -     */
> > -    if (mount(NULL, "/", NULL, MS_REC | MS_SLAVE, NULL) < 0) {
> > -        fuse_log(FUSE_LOG_ERR, "mount(/, MS_REC|MS_SLAVE): %m\n");
> > -        exit(1);
> > -    }
> > +    if (lo->mount_ns) {
> > +        /*
> > +         * If the mounts have shared propagation then we want to opt
> out so our
> > +         * mount changes don't affect the parent mount namespace.
> > +         */
> > +        if (mount(NULL, "/", NULL, MS_REC | MS_SLAVE, NULL) < 0) {
> > +            fuse_log(FUSE_LOG_ERR, "mount(/, MS_REC|MS_SLAVE): %m\n");
> > +            exit(1);
> > +        }
> >
> > -    /* The child must remount /proc to use the new pid namespace */
> > -    if (mount("proc", "/proc", "proc",
> > -              MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_RELATIME, NULL) <
> 0) {
> > -        fuse_log(FUSE_LOG_ERR, "mount(/proc): %m\n");
> > -        exit(1);
> > -    }
> > +        /* The child must remount /proc to use the new pid namespace */
> > +        if (mount("proc", "/proc", "proc",
> > +                  MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_RELATIME, NULL)
> < 0) {
> > +            fuse_log(FUSE_LOG_ERR, "mount(/proc): %m\n");
> > +            exit(1);
> > +        }
> >
> > -    /*
> > -     * We only need /proc/self/fd. Prevent ".." from accessing parent
> > -     * directories of /proc/self/fd by bind-mounting it over /proc.
> Since / was
> > -     * previously remounted with MS_REC | MS_SLAVE this mount change
> only
> > -     * affects our process.
> > -     */
> > -    if (mount("/proc/self/fd", "/proc", NULL, MS_BIND, NULL) < 0) {
> > -        fuse_log(FUSE_LOG_ERR, "mount(/proc/self/fd, MS_BIND): %m\n");
> > -        exit(1);
> > -    }
> > +        /*
> > +         * We only need /proc/self/fd. Prevent ".." from accessing
> parent
> > +         * directories of /proc/self/fd by bind-mounting it over /proc.
> Since
> > +         * / was previously remounted with MS_REC | MS_SLAVE this mount
> change
> > +         * only affects our process.
> > +         */
> > +        if (mount("/proc/self/fd", "/proc", NULL, MS_BIND, NULL) < 0) {
> > +            fuse_log(FUSE_LOG_ERR, "mount(/proc/self/fd, MS_BIND):
> %m\n");
> > +            exit(1);
> > +        }
> >
> > -    /* Get the /proc (actually /proc/self/fd, see above) file
> descriptor */
> > -    lo->proc_self_fd = open("/proc", O_PATH);
> > -    if (lo->proc_self_fd == -1) {
> > -        fuse_log(FUSE_LOG_ERR, "open(/proc, O_PATH): %m\n");
> > -        exit(1);
> > +        /* Get the /proc (actually /proc/self/fd, see above) file
> descriptor */
> > +        lo->proc_self_fd = open("/proc", O_PATH);
> > +        if (lo->proc_self_fd == -1) {
> > +            fuse_log(FUSE_LOG_ERR, "open(/proc, O_PATH): %m\n");
> > +            exit(1);
> > +        }
> > +    } else {
> > +        /* Now we can get our /proc/self/fd directory file descriptor */
> > +        lo->proc_self_fd = open("/proc/self/fd", O_PATH);
> > +        if (lo->proc_self_fd == -1) {
> > +            fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n");
> > +            exit(1);
> > +        }
> >      }
> >  }
> >
> > @@ -3347,7 +3368,9 @@ static void setup_sandbox(struct lo_data *lo,
> struct fuse_session *se,
> >  {
> >      if (lo->sandbox == SANDBOX_NAMESPACE) {
> >          setup_namespaces(lo, se);
> > -        setup_mounts(lo->source);
> > +        if (lo->mount_ns) {
> > +            setup_mounts(lo->source);
> > +        }
> >      } else {
> >          setup_chroot(lo);
> >      }
> > @@ -3438,7 +3461,11 @@ static void setup_root(struct lo_data *lo, struct
> lo_inode *root)
> >      struct stat stat;
> >      uint64_t mnt_id;
> >
> > -    fd = open("/", O_PATH);
> > +    if (lo->mount_ns) {
> > +        fd = open("/", O_PATH);
> > +    } else {
> > +        fd = open(lo->source, O_PATH);
> > +    }
> >      if (fd == -1) {
> >          fuse_log(FUSE_LOG_ERR, "open(%s, O_PATH): %m\n", lo->source);
> >          exit(1);
> > @@ -3515,6 +3542,9 @@ int main(int argc, char *argv[])
> >      lo.allow_direct_io = 0,
> >      lo.proc_self_fd = -1;
> >
> > +    lo.reconnect = 0;
> > +    lo.mount_ns = 1;
> > +
> >      /* Don't mask creation mode, kernel already did that */
> >      umask(0);
> >
> > @@ -3577,6 +3607,22 @@ int main(int argc, char *argv[])
> >          goto err_out1;
> >      }
> >
> > +    /* For sandbox mode "chroot", set the mount_ns option to 0. */
> > +    if (lo.sandbox == SANDBOX_CHROOT) {
> > +        lo.mount_ns = 0;
> > +    }
> > +
> > +    if (lo.reconnect) {
> > +        if ((lo.sandbox == SANDBOX_NAMESPACE && lo.mount_ns) || lo.flock
> > +                                               || lo.posix_lock ||
> lo.xattr) {
> > +            printf("Mount namespace, remote lock, and extended
> attributes"
> > +                   " are not supported by reconnection (-o reconnect).
> Please "
> > +                   "specify  -o no_mount_ns, -o no_flock (default), -o"
> > +                   "no_posix_lock (default), and -o no_xattr
> (default).\n");
> > +            exit(1);
> > +        }
> > +    }
> > +
> >      if (opts.log_level != 0) {
> >          current_log_level = opts.log_level;
> >      } else {
> > --
> > 2.20.1
> >
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>
>

[-- Attachment #2: Type: text/html, Size: 16924 bytes --]