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virtiofsd: Announce sub-mount points

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Whenever we encounter a directory with an st_dev that differs from that
of its parent, we set the FUSE_ATTR_SUBMOUNT flag so the guest can
create a submount for it.

Make this behavior 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.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200909184028.262297-7-mreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
  Manual merge
This commit is contained in:
Max Reitz 2020-09-09 20:40:26 +02:00 committed by Dr. David Alan Gilbert
parent eba8b096c1
commit 08dce386e7
2 changed files with 60 additions and 8 deletions
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1
tools/virtiofsd/helper.c
View File

@ -178,6 +178,7 @@ void fuse_cmdline_help(void)
" default: depends on cache= option.\n"
" -o writeback|no_writeback enable/disable writeback cache\n"
" default: no_writeback\n"
" -o announce_submounts Announce sub-mount points to the guest\n"
" -o xattr|no_xattr enable/disable xattr\n"
" default: no_xattr\n"
" -o modcaps=CAPLIST Modify the list of capabilities\n"

67
tools/virtiofsd/passthrough_ll.c
View File

@ -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>
@ -173,6 +174,7 @@ struct lo_data {
int timeout_set;
int readdirplus_set;
int readdirplus_clear;
int announce_submounts;
int allow_direct_io;
struct lo_inode root;
GHashTable *inodes; /* protected by lo->mutex */
@ -211,6 +213,7 @@ static const struct fuse_opt lo_opts[] = {
{ "cache=always", offsetof(struct lo_data, cache), CACHE_ALWAYS },
{ "readdirplus", offsetof(struct lo_data, readdirplus_set), 1 },
{ "no_readdirplus", offsetof(struct lo_data, readdirplus_clear), 1 },
{ "announce_submounts", offsetof(struct lo_data, announce_submounts), 1 },
{ "allow_direct_io", offsetof(struct lo_data, allow_direct_io), 1 },
{ "no_allow_direct_io", offsetof(struct lo_data, allow_direct_io), 0 },
FUSE_OPT_END
@ -608,22 +611,52 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn)
}
}
/**
* Call fstatat() and set st_rdev whenever a directory's st_dev
* differs from the rparent's st_dev (@parent_dev). This will
* announce submounts to the FUSE client (unless @announce_submounts
* is false).
*/
static int do_fstatat(int dirfd, const char *pathname, struct stat *statbuf,
int flags, dev_t parent_dev, uint32_t *fuse_attr_flags)
{
int res = fstatat(dirfd, pathname, statbuf, flags);
if (res == -1) {
return res;
}
if (statbuf->st_dev != parent_dev && S_ISDIR(statbuf->st_mode) &&
fuse_attr_flags)
{
*fuse_attr_flags |= FUSE_ATTR_SUBMOUNT;
}
return 0;
}
static void lo_getattr(fuse_req_t req, fuse_ino_t ino,
struct fuse_file_info *fi)
{
int res;
struct stat buf;
struct lo_data *lo = lo_data(req);
struct lo_inode *inode = lo_inode(req, ino);
uint32_t fuse_attr_flags = 0;
(void)fi;
res =
fstatat(lo_fd(req, ino), "", &buf, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
res = do_fstatat(inode->fd, "", &buf, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW,
inode->parent_dev, &fuse_attr_flags);
lo_inode_put(lo, &inode);
if (res == -1) {
return (void)fuse_reply_err(req, errno);
}
fuse_reply_attr(req, &buf, lo->timeout);
if (!lo->announce_submounts) {
fuse_attr_flags &= ~FUSE_ATTR_SUBMOUNT;
}
fuse_reply_attr_with_flags(req, &buf, lo->timeout, fuse_attr_flags);
}
static int lo_fi_fd(fuse_req_t req, struct fuse_file_info *fi)
@ -819,11 +852,16 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name,
goto out_err;
}
res = fstatat(newfd, "", &e->attr, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
res = do_fstatat(newfd, "", &e->attr, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW,
dir->key.dev, &e->attr_flags);
if (res == -1) {
goto out_err;
}
if (!lo->announce_submounts) {
e->attr_flags &= ~FUSE_ATTR_SUBMOUNT;
}
inode = lo_find(lo, &e->attr);
if (inode) {
close(newfd);
@ -1069,11 +1107,17 @@ static void lo_link(fuse_req_t req, fuse_ino_t ino, fuse_ino_t parent,
goto out_err;
}
res = fstatat(inode->fd, "", &e.attr, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
res = do_fstatat(inode->fd, "", &e.attr,
AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW,
parent_inode->key.dev, &e.attr_flags);
if (res == -1) {
goto out_err;
}
if (!lo->announce_submounts) {
e.attr_flags &= ~FUSE_ATTR_SUBMOUNT;
}
pthread_mutex_lock(&lo->mutex);
inode->nlookup++;
pthread_mutex_unlock(&lo->mutex);
@ -1108,14 +1152,21 @@ static struct lo_inode *lookup_name(fuse_req_t req, fuse_ino_t parent,
{
int res;
struct stat attr;
struct lo_data *lo = lo_data(req);
struct lo_inode *dir = lo_inode(req, parent);
res = fstatat(lo_fd(req, parent), name, &attr,
AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
if (!dir) {
return NULL;
}
res = do_fstatat(dir->fd, name, &attr,
AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW, dir->key.dev, NULL);
lo_inode_put(lo, &dir);
if (res == -1) {
return NULL;
}
return lo_find(lo_data(req), &attr);
return lo_find(lo, &attr);
}
static void lo_rmdir(fuse_req_t req, fuse_ino_t parent, const char *name)