From: Max Reitz <mreitz@redhat.com>
Whenever we encounter a directory with an st_dev or mount ID that
differs from that of its parent, we set the FUSE_ATTR_SUBMOUNT flag so
the guest can create a submount for it.
We only need to do so in lo_do_lookup(). The following functions return
a fuse_attr object:
- lo_create(), though fuse_reply_create(): Calls lo_do_lookup().
- lo_lookup(), though fuse_reply_entry(): Calls lo_do_lookup().
- lo_mknod_symlink(), through fuse_reply_entry(): Calls lo_do_lookup().
- lo_link(), through fuse_reply_entry(): Creating a link cannot create a
submount, so there is no need to check for it.
- lo_getattr(), through fuse_reply_attr(): Announcing submounts when the
node is first detected (at lookup) is sufficient. We do not need to
return the submount attribute later.
- lo_do_readdir(), through fuse_add_direntry_plus(): Calls
lo_do_lookup().
Make announcing submounts optional, so submounts are only announced to
the guest with the announce_submounts option. Some users may prefer the
current behavior, so that the guest learns nothing about the host mount
structure.
(announce_submounts is force-disabled when the guest does not present
the FUSE_SUBMOUNTS capability, or when there is no statx().)
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20201102161859.156603-6-mreitz@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
tools/virtiofsd/helper.c | 1 +
tools/virtiofsd/passthrough_ll.c | 22 ++++++++++++++++++++++
2 files changed, 23 insertions(+)
diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c
index ae1b22e4a6..75ac48dec2 100644
--- a/tools/virtiofsd/helper.c
+++ b/tools/virtiofsd/helper.c
@@ -190,6 +190,7 @@ void fuse_cmdline_help(void)
" retain/discard O_DIRECT flags passed down\n"
" to virtiofsd from guest applications.\n"
" default: no_allow_direct_io\n"
+ " -o announce_submounts Announce sub-mount points to the guest\n"
);
}
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 34d107975f..ec1008bceb 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -40,6 +40,7 @@
#include "fuse_virtio.h"
#include "fuse_log.h"
#include "fuse_lowlevel.h"
+#include "standard-headers/linux/fuse.h"
#include <assert.h>
#include <cap-ng.h>
#include <dirent.h>
@@ -167,6 +168,7 @@ struct lo_data {
int readdirplus_set;
int readdirplus_clear;
int allow_direct_io;
+ int announce_submounts;
bool use_statx;
struct lo_inode root;
GHashTable *inodes; /* protected by lo->mutex */
@@ -207,6 +209,7 @@ static const struct fuse_opt lo_opts[] = {
{ "no_readdirplus", offsetof(struct lo_data, readdirplus_clear), 1 },
{ "allow_direct_io", offsetof(struct lo_data, allow_direct_io), 1 },
{ "no_allow_direct_io", offsetof(struct lo_data, allow_direct_io), 0 },
+ { "announce_submounts", offsetof(struct lo_data, announce_submounts), 1 },
FUSE_OPT_END
};
static bool use_syslog = false;
@@ -601,6 +604,20 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn)
fuse_log(FUSE_LOG_DEBUG, "lo_init: disabling readdirplus\n");
conn->want &= ~FUSE_CAP_READDIRPLUS;
}
+
+ if (!(conn->capable & FUSE_CAP_SUBMOUNTS) && lo->announce_submounts) {
+ fuse_log(FUSE_LOG_WARNING, "lo_init: Cannot announce submounts, client "
+ "does not support it\n");
+ lo->announce_submounts = false;
+ }
+
+#ifndef CONFIG_STATX
+ if (lo->announce_submounts) {
+ fuse_log(FUSE_LOG_WARNING, "lo_init: Cannot announce submounts, there "
+ "is no statx()\n");
+ lo->announce_submounts = false;
+ }
+#endif
}
static void lo_getattr(fuse_req_t req, fuse_ino_t ino,
@@ -877,6 +894,11 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name,
goto out_err;
}
+ if (S_ISDIR(e->attr.st_mode) && lo->announce_submounts &&
+ (e->attr.st_dev != dir->key.dev || mnt_id != dir->key.mnt_id)) {
+ e->attr_flags |= FUSE_ATTR_SUBMOUNT;
+ }
+
inode = lo_find(lo, &e->attr, mnt_id);
if (inode) {
close(newfd);
--
2.28.0