From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_2 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 94515C3A59B for ; Fri, 30 Aug 2019 13:48:57 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 54F4E23405 for ; Fri, 30 Aug 2019 13:48:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 54F4E23405 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kaod.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:58968 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i3hGq-0003zn-Es for qemu-devel@archiver.kernel.org; Fri, 30 Aug 2019 09:48:56 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48798) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i3h74-000615-B2 for qemu-devel@nongnu.org; Fri, 30 Aug 2019 09:38:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i3h70-00061h-Uv for qemu-devel@nongnu.org; Fri, 30 Aug 2019 09:38:49 -0400 Received: from 4.mo178.mail-out.ovh.net ([46.105.49.171]:42150) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i3h70-0005hq-IG for qemu-devel@nongnu.org; Fri, 30 Aug 2019 09:38:46 -0400 Received: from player158.ha.ovh.net (unknown [10.109.159.123]) by mo178.mail-out.ovh.net (Postfix) with ESMTP id B32AB77262 for ; Fri, 30 Aug 2019 14:22:45 +0200 (CEST) Received: from kaod.org (lns-bzn-46-82-253-208-248.adsl.proxad.net [82.253.208.248]) (Authenticated sender: groug@kaod.org) by player158.ha.ovh.net (Postfix) with ESMTPSA id 6491292BFBE4; Fri, 30 Aug 2019 12:22:39 +0000 (UTC) Date: Fri, 30 Aug 2019 14:22:38 +0200 From: Greg Kurz To: Christian Schoenebeck Message-ID: <20190830142238.4dbf65c8@bahia.lan> In-Reply-To: <50fc6fbbfd80c25d2ad1752fb945cdfc7d847f20.1566503584.git.qemu_oss@crudebyte.com> References: <50fc6fbbfd80c25d2ad1752fb945cdfc7d847f20.1566503584.git.qemu_oss@crudebyte.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Ovh-Tracer-Id: 1519120451097893184 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: -100 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgeduvddrudeigedghedvucetufdoteggodetrfdotffvucfrrhhofhhilhgvmecuqfggjfdpvefjgfevmfevgfenuceurghilhhouhhtmecuhedttdenucesvcftvggtihhpihgvnhhtshculddquddttddm X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 46.105.49.171 Subject: Re: [Qemu-devel] [PATCH v6 2/4] 9p: Added virtfs option 'multidevs=remap|forbid|warn' X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Stefan Hajnoczi , "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" , qemu-devel@nongnu.org, Antonios Motakis , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, 22 Aug 2019 21:33:37 +0200 Christian Schoenebeck wrote: > 'warn' (default): Only log an error message (once) on host if more than one > device is shared by same export, except of that just ignore this config > error though. This is the default behaviour for not breaking existing > installations implying that they really know what they are doing. > > 'forbid': Like 'warn', but except of just logging an error this > also denies access of guest to additional devices. > > 'remap': Allows to share more than one device per export by remapping > inodes from host to guest appropriately. To support multiple devices on the > 9p share, and avoid qid path collisions we take the device id as input to > generate a unique QID path. The lowest 48 bits of the path will be set > equal to the file inode, and the top bits will be uniquely assigned based > on the top 16 bits of the inode and the device id. > > Signed-off-by: Antonios Motakis > [CS: - Rebased to https://github.com/gkurz/qemu/commits/9p-next > (SHA1 177fd3b6a8). > - Updated hash calls to new xxhash API. > - Added virtfs option 'multidevs', original patch simply did the inode > remapping without being asked. > - Updated docs for new option 'multidevs'. > - Capture root_ino in v9fs_device_realize_common() as well, not just > the device id. > - Fixed v9fs_do_readdir() not having remapped inodes. > - Log error message when running out of prefixes in > qid_path_prefixmap(). > - Fixed definition of QPATH_INO_MASK. > - Dropped unnecessary parantheses in qpp_lookup_func(). > - Dropped unnecessary g_malloc0() result checks. ] > Signed-off-by: Christian Schoenebeck > --- Some more comments below. > fsdev/file-op-9p.h | 5 ++ > fsdev/qemu-fsdev-opts.c | 7 +- > fsdev/qemu-fsdev.c | 11 +++ > hw/9pfs/9p.c | 182 ++++++++++++++++++++++++++++++++++++++++++------ > hw/9pfs/9p.h | 13 ++++ > qemu-options.hx | 33 +++++++-- > vl.c | 6 +- > 7 files changed, 229 insertions(+), 28 deletions(-) > > diff --git a/fsdev/file-op-9p.h b/fsdev/file-op-9p.h > index c757c8099f..f2f7772c86 100644 > --- a/fsdev/file-op-9p.h > +++ b/fsdev/file-op-9p.h > @@ -59,6 +59,11 @@ typedef struct ExtendedOps { > #define V9FS_RDONLY 0x00000040 > #define V9FS_PROXY_SOCK_FD 0x00000080 > #define V9FS_PROXY_SOCK_NAME 0x00000100 > +/* > + * multidevs option (either one of the two applies exclusively) > + */ > +#define V9FS_REMAP_INODES 0x00000200 > +#define V9FS_FORBID_MULTIDEVS 0x00000400 > > #define V9FS_SEC_MASK 0x0000003C > > diff --git a/fsdev/qemu-fsdev-opts.c b/fsdev/qemu-fsdev-opts.c > index 7c31ffffaf..07a18c6e48 100644 > --- a/fsdev/qemu-fsdev-opts.c > +++ b/fsdev/qemu-fsdev-opts.c > @@ -31,7 +31,9 @@ static QemuOptsList qemu_fsdev_opts = { > }, { > .name = "readonly", > .type = QEMU_OPT_BOOL, > - > + }, { > + .name = "multidevs", > + .type = QEMU_OPT_STRING, > }, { > .name = "socket", > .type = QEMU_OPT_STRING, > @@ -76,6 +78,9 @@ static QemuOptsList qemu_virtfs_opts = { > .name = "readonly", > .type = QEMU_OPT_BOOL, > }, { > + .name = "multidevs", > + .type = QEMU_OPT_STRING, > + }, { > .name = "socket", > .type = QEMU_OPT_STRING, > }, { > diff --git a/fsdev/qemu-fsdev.c b/fsdev/qemu-fsdev.c > index 077a8c4e2b..ed03d559a9 100644 > --- a/fsdev/qemu-fsdev.c > +++ b/fsdev/qemu-fsdev.c > @@ -58,6 +58,7 @@ static FsDriverTable FsDrivers[] = { > "writeout", > "fmode", > "dmode", > + "multidevs", > "throttling.bps-total", > "throttling.bps-read", > "throttling.bps-write", > @@ -121,6 +122,7 @@ int qemu_fsdev_add(QemuOpts *opts, Error **errp) > const char *fsdev_id = qemu_opts_id(opts); > const char *fsdriver = qemu_opt_get(opts, "fsdriver"); > const char *writeout = qemu_opt_get(opts, "writeout"); > + const char *multidevs = qemu_opt_get(opts, "multidevs"); > bool ro = qemu_opt_get_bool(opts, "readonly", 0); > > if (!fsdev_id) { > @@ -161,6 +163,15 @@ int qemu_fsdev_add(QemuOpts *opts, Error **errp) > } else { > fsle->fse.export_flags &= ~V9FS_RDONLY; > } > + if (multidevs) { > + if (!strcmp(multidevs, "remap")) { > + fsle->fse.export_flags &= ~V9FS_FORBID_MULTIDEVS; > + fsle->fse.export_flags |= V9FS_REMAP_INODES; > + } else if (!strcmp(multidevs, "forbid")) { > + fsle->fse.export_flags &= ~V9FS_REMAP_INODES; > + fsle->fse.export_flags |= V9FS_FORBID_MULTIDEVS; > + } > + } > > if (fsle->fse.ops->parse_opts) { > if (fsle->fse.ops->parse_opts(opts, &fsle->fse, errp)) { > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c > index 8cc65c2c67..c96ea51116 100644 > --- a/hw/9pfs/9p.c > +++ b/hw/9pfs/9p.c > @@ -25,6 +25,7 @@ > #include "trace.h" > #include "migration/blocker.h" > #include "sysemu/qtest.h" > +#include "qemu/xxhash.h" > > int open_fd_hw; > int total_open_fd; > @@ -571,22 +572,109 @@ static void coroutine_fn virtfs_reset(V9fsPDU *pdu) > P9_STAT_MODE_NAMED_PIPE | \ > P9_STAT_MODE_SOCKET) > > -/* This is the algorithm from ufs in spfs */ > + > +/* creative abuse of tb_hash_func7, which is based on xxhash */ > +static uint32_t qpp_hash(QppEntry e) > +{ > + return qemu_xxhash7(e.ino_prefix, e.dev, 0, 0, 0); > +} > + > +static bool qpp_lookup_func(const void *obj, const void *userp) > +{ > + const QppEntry *e1 = obj, *e2 = userp; > + return e1->dev == e2->dev && e1->ino_prefix == e2->ino_prefix; > +} > + > +static void qpp_table_remove(void *p, uint32_t h, void *up) > +{ > + g_free(p); > +} > + > +static void qpp_table_destroy(struct qht *ht) > +{ > + qht_iter(ht, qpp_table_remove, NULL); > + qht_destroy(ht); > +} > + > +/* stat_to_qid needs to map inode number (64 bits) and device id (32 bits) > + * to a unique QID path (64 bits). To avoid having to map and keep track > + * of up to 2^64 objects, we map only the 16 highest bits of the inode plus > + * the device id to the 16 highest bits of the QID path. The 48 lowest bits > + * of the QID path equal to the lowest bits of the inode number. > + * > + * This takes advantage of the fact that inode number are usually not > + * random but allocated sequentially, so we have fewer items to keep > + * track of. > + */ > +static int qid_path_prefixmap(V9fsPDU *pdu, const struct stat *stbuf, > + uint64_t *path) > +{ > + QppEntry lookup = { > + .dev = stbuf->st_dev, > + .ino_prefix = (uint16_t) (stbuf->st_ino >> 48) > + }, *val; > + uint32_t hash = qpp_hash(lookup); > + > + val = qht_lookup(&pdu->s->qpp_table, &lookup, hash); > + > + if (!val) { > + if (pdu->s->qp_prefix_next == 0) { > + /* we ran out of prefixes */ > + error_report_once( > + "9p: No more prefixes available for remapping inodes from " > + "host to guest." > + ); > + return -ENFILE; > + } > + > + val = g_malloc0(sizeof(QppEntry)); > + *val = lookup; > + > + /* new unique inode prefix and device combo */ > + val->qp_prefix = pdu->s->qp_prefix_next++; > + qht_insert(&pdu->s->qpp_table, val, hash, NULL); > + } > + > + *path = ((uint64_t)val->qp_prefix << 48) | (stbuf->st_ino & QPATH_INO_MASK); > + return 0; > +} > + > static int stat_to_qid(V9fsPDU *pdu, const struct stat *stbuf, V9fsQID *qidp) > { > + int err; > size_t size; > > - if (pdu->s->dev_id != stbuf->st_dev) { > - error_report_once( > - "9p: Multiple devices detected in same VirtFS export. " > - "You must use a separate export for each device." > - ); > - return -ENODEV; > + if (pdu->s->ctx.export_flags & V9FS_REMAP_INODES) { > + /* map inode+device to qid path (fast path) */ > + err = qid_path_prefixmap(pdu, stbuf, &qidp->path); > + if (err) { > + return err; > + } > + } else { > + if (pdu->s->dev_id != stbuf->st_dev) { > + if (pdu->s->ctx.export_flags & V9FS_FORBID_MULTIDEVS) { > + error_report_once( > + "9p: Multiple devices detected in same VirtFS export. " > + "Access of guest to additional devices is (partly) " > + "denied due to virtfs option 'multidevs=forbid' being " > + "effective." > + ); > + return -ENODEV; > + } else { > + error_report_once( > + "9p: Multiple devices detected in same VirtFS export, " > + "which might lead to file ID collisions and severe " > + "misbehaviours on guest! You should either use a " > + "separate export for each device shared from host or " > + "use virtfs option 'multidevs=remap'!" > + ); > + } > + } > + memset(&qidp->path, 0, sizeof(qidp->path)); > + size = MIN(sizeof(stbuf->st_ino), sizeof(qidp->path)); > + memcpy(&qidp->path, &stbuf->st_ino, size); > } > > - memset(&qidp->path, 0, sizeof(qidp->path)); > - size = MIN(sizeof(stbuf->st_ino), sizeof(qidp->path)); > - memcpy(&qidp->path, &stbuf->st_ino, size); > qidp->version = stbuf->st_mtime ^ (stbuf->st_size << 8); > qidp->type = 0; > if (S_ISDIR(stbuf->st_mode)) { > @@ -616,6 +704,30 @@ static int coroutine_fn fid_to_qid(V9fsPDU *pdu, V9fsFidState *fidp, > return 0; > } > > +static int coroutine_fn dirent_to_qid(V9fsPDU *pdu, V9fsFidState *fidp, > + struct dirent *dent, V9fsQID *qidp) > +{ > + struct stat stbuf; > + V9fsPath path; > + int err; > + > + v9fs_path_init(&path); > + > + err = v9fs_co_name_to_path(pdu, &fidp->path, dent->d_name, &path); > + if (err < 0) { > + goto out; > + } > + err = v9fs_co_lstat(pdu, &path, &stbuf); > + if (err < 0) { > + goto out; > + } > + err = stat_to_qid(pdu, &stbuf, qidp); > + > +out: > + v9fs_path_free(&path); > + return err; > +} > + > V9fsPDU *pdu_alloc(V9fsState *s) > { > V9fsPDU *pdu = NULL; > @@ -1964,16 +2076,39 @@ static int coroutine_fn v9fs_do_readdir(V9fsPDU *pdu, V9fsFidState *fidp, > v9fs_string_free(&name); > return count; > } > - /* > - * Fill up just the path field of qid because the client uses > - * only that. To fill the entire qid structure we will have > - * to stat each dirent found, which is expensive > - */ > - size = MIN(sizeof(dent->d_ino), sizeof(qid.path)); > - memcpy(&qid.path, &dent->d_ino, size); > - /* Fill the other fields with dummy values */ > - qid.type = 0; > - qid.version = 0; > + > + if (pdu->s->ctx.export_flags & V9FS_REMAP_INODES) { > + /* > + * dirent_to_qid() implies expensive stat call for each entry, > + * we must do that here though since inode remapping requires > + * the device id, which in turn might be different for > + * different entries; we cannot make any assumption to avoid > + * that here. > + */ > + err = dirent_to_qid(pdu, fidp, dent, &qid); > + if (err < 0) { > + v9fs_readdir_unlock(&fidp->fs.dir); > + v9fs_co_seekdir(pdu, fidp, saved_dir_pos); > + v9fs_string_free(&name); > + return err; > + } > + } else { > + /* > + * Fill up just the path field of qid because the client uses > + * only that. To fill the entire qid structure we will have > + * to stat each dirent found, which is expensive. For the > + * latter reason we don't call dirent_to_qid() here. Only drawback > + * is that no multi-device export detection of stat_to_qid() > + * would be done and provided as error to the user here. But > + * user would get that error anyway when accessing those > + * files/dirs through other ways. > + */ > + size = MIN(sizeof(dent->d_ino), sizeof(qid.path)); > + memcpy(&qid.path, &dent->d_ino, size); > + /* Fill the other fields with dummy values */ > + qid.type = 0; > + qid.version = 0; > + } > > /* 11 = 7 + 4 (7 = start offset, 4 = space for storing count) */ > len = pdu_marshal(pdu, 11 + count, "Qqbs", > @@ -3672,8 +3807,13 @@ int v9fs_device_realize_common(V9fsState *s, const V9fsTransport *t, > goto out; > } > > + s->root_ino = stat.st_ino; This isn't used anywhere. It looks like a leftover of the readdir fix in v5. > s->dev_id = stat.st_dev; > > + /* QID path hash table. 1 entry ought to be enough for anybody ;) */ > + qht_init(&s->qpp_table, qpp_lookup_func, 1, QHT_MODE_AUTO_RESIZE); > + s->qp_prefix_next = 1; /* reserve 0 to detect overflow */ > + > s->ctx.fst = &fse->fst; > fsdev_throttle_init(s->ctx.fst); > > @@ -3687,6 +3827,7 @@ out: > } > g_free(s->tag); > g_free(s->ctx.fs_root); > + qpp_table_destroy(&s->qpp_table); > v9fs_path_free(&path); > } > return rc; > @@ -3699,6 +3840,7 @@ void v9fs_device_unrealize_common(V9fsState *s, Error **errp) > } > fsdev_throttle_cleanup(s->ctx.fst); > g_free(s->tag); > + qpp_table_destroy(&s->qpp_table); > g_free(s->ctx.fs_root); > } > > diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h > index 5e316178d5..a283b0193e 100644 > --- a/hw/9pfs/9p.h > +++ b/hw/9pfs/9p.h > @@ -8,6 +8,7 @@ > #include "fsdev/9p-iov-marshal.h" > #include "qemu/thread.h" > #include "qemu/coroutine.h" > +#include "qemu/qht.h" > > enum { > P9_TLERROR = 6, > @@ -235,6 +236,15 @@ struct V9fsFidState > V9fsFidState *rclm_lst; > }; > > +#define QPATH_INO_MASK ((1ULL << 48) - 1) > + > +/* QID path prefix entry, see stat_to_qid */ > +typedef struct { > + dev_t dev; > + uint16_t ino_prefix; > + uint16_t qp_prefix; > +} QppEntry; > + > struct V9fsState > { > QLIST_HEAD(, V9fsPDU) free_list; > @@ -256,7 +266,10 @@ struct V9fsState > Error *migration_blocker; > V9fsConf fsconf; > V9fsQID root_qid; > + ino_t root_ino; Thinking again, I'm wondering if root_ino and dev_id could be used instead of root_qid in v9fs_walk()... Would you have a look at that if you decide to fix the readdir issue ? > dev_t dev_id; > + struct qht qpp_table; > + uint16_t qp_prefix_next; > }; > > /* 9p2000.L open flags */ > diff --git a/qemu-options.hx b/qemu-options.hx > index 9621e934c0..603e5e8e15 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -1335,17 +1335,17 @@ ETEXI > > DEF("virtfs", HAS_ARG, QEMU_OPTION_virtfs, > "-virtfs local,path=path,mount_tag=tag,security_model=mapped-xattr|mapped-file|passthrough|none\n" > - " [,id=id][,writeout=immediate][,readonly][,fmode=fmode][,dmode=dmode]\n" > - "-virtfs proxy,mount_tag=tag,socket=socket[,id=id][,writeout=immediate][,readonly]\n" > - "-virtfs proxy,mount_tag=tag,sock_fd=sock_fd[,id=id][,writeout=immediate][,readonly]\n" > + " [,id=id][,writeout=immediate][,readonly][,fmode=fmode][,dmode=dmode][,multidevs=remap|forbid|warn]\n" > + "-virtfs proxy,mount_tag=tag,socket=socket[,id=id][,writeout=immediate][,readonly][,multidevs=remap|forbid|warn]\n" > + "-virtfs proxy,mount_tag=tag,sock_fd=sock_fd[,id=id][,writeout=immediate][,readonly][,multidevs=remap|forbid|warn]\n" > "-virtfs synth,mount_tag=tag[,id=id][,readonly]\n", > QEMU_ARCH_ALL) > > STEXI > > -@item -virtfs local,path=@var{path},mount_tag=@var{mount_tag} ,security_model=@var{security_model}[,writeout=@var{writeout}][,readonly] [,fmode=@var{fmode}][,dmode=@var{dmode}] > -@itemx -virtfs proxy,socket=@var{socket},mount_tag=@var{mount_tag} [,writeout=@var{writeout}][,readonly] > -@itemx -virtfs proxy,sock_fd=@var{sock_fd},mount_tag=@var{mount_tag} [,writeout=@var{writeout}][,readonly] > +@item -virtfs local,path=@var{path},mount_tag=@var{mount_tag} ,security_model=@var{security_model}[,writeout=@var{writeout}][,readonly] [,fmode=@var{fmode}][,dmode=@var{dmode}][,multidevs=@var{multidevs}] > +@itemx -virtfs proxy,socket=@var{socket},mount_tag=@var{mount_tag} [,writeout=@var{writeout}][,readonly][,multidevs=@var{multidevs}] > +@itemx -virtfs proxy,sock_fd=@var{sock_fd},mount_tag=@var{mount_tag} [,writeout=@var{writeout}][,readonly][,multidevs=@var{multidevs}] > @itemx -virtfs synth,mount_tag=@var{mount_tag} > @findex -virtfs > > @@ -1399,6 +1399,27 @@ Specifies the default mode for newly created directories on the host. Works > only with security models "mapped-xattr" and "mapped-file". > @item mount_tag=@var{mount_tag} > Specifies the tag name to be used by the guest to mount this export point. > +@item multidevs=@var{multidevs} > +Specifies how to deal with multiple devices being shared with a 9p export. > +Supported behaviours are either "remap", "forbid" or "warn". The latter is > +the default behaviour on which virtfs 9p expects only one device to be > +shared with the same export, and if more than one device is shared and > +accessed via the same 9p export then only a warning message is logged > +(once) by qemu on host side. In order to avoid file ID collisions on guest > +you should either create a separate virtfs export for each device to be > +shared with guests (recommended way) or you might use "remap" instead which > +allows you to share multiple devices with only one export instead, which is > +achieved by remapping the original inode numbers from host to guest in a > +way that would prevent such collisions. Remapping inodes in such use cases > +is required because the original device IDs from host are never passed and > +exposed on guest. Instead all files of an export shared with virtfs always > +share the same device id on guest. So two files with identical inode > +numbers but from actually different devices on host would otherwise cause a > +file ID collision and hence potential misbehaviours on guest. "forbid" on > +the other hand assumes like "warn" that only one device is shared by the > +same export, however it will not only log a warning message but also > +deny access to additional devices on guest. Note though that "forbid" does > +currently not block all possible file access operations. > @end table > ETEXI > > diff --git a/vl.c b/vl.c > index b426b32134..9cb29b483d 100644 > --- a/vl.c > +++ b/vl.c > @@ -3320,7 +3320,7 @@ int main(int argc, char **argv, char **envp) > case QEMU_OPTION_virtfs: { > QemuOpts *fsdev; > QemuOpts *device; > - const char *writeout, *sock_fd, *socket, *path, *security_model; > + const char *writeout, *sock_fd, *socket, *path, *security_model, *multidevs; > > olist = qemu_find_opts("virtfs"); > if (!olist) { > @@ -3380,6 +3380,10 @@ int main(int argc, char **argv, char **envp) > qemu_opt_set_bool(fsdev, "readonly", > qemu_opt_get_bool(opts, "readonly", 0), > &error_abort); > + multidevs = qemu_opt_get(opts, "multidevs"); > + if (multidevs) { > + qemu_opt_set(fsdev, "multidevs", multidevs, &error_abort); > + } > device = qemu_opts_create(qemu_find_opts("device"), NULL, 0, > &error_abort); > qemu_opt_set(device, "driver", "virtio-9p-pci", &error_abort);