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

[Jiachen Zhang]

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".

  - 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".

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