From 9d82f6a3e68c2986633ad11687da2193e9acb0cb Mon Sep 17 00:00:00 2001 From: Max Reitz Date: Mon, 2 Nov 2020 17:18:57 +0100 Subject: [PATCH] virtiofsd: Announce sub-mount points 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 Reviewed-by: Stefan Hajnoczi Message-Id: <20201102161859.156603-6-mreitz@redhat.com> Signed-off-by: Dr. David Alan Gilbert --- 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 #include #include @@ -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); -- 2.11.4.GIT