On Wed, 26 Jun 2019 20:42:13 +0200 Christian Schoenebeck via Qemu-devel <qemu-devel@nongnu.org> wrote:
> 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 <antonios.mota...@huawei.com> Same remark about changes to the original patch. BTW, I had a concern with the way v9fs_do_readdir() open-codes QID generation without calling stat_to_qid(). See discussion here: https://lists.gnu.org/archive/html/qemu-devel/2018-02/msg02724.html I guess you should ensure in a preliminary patch that QIDs only come out of stat_to_qid(). > Signed-off-by: Christian Schoenebeck <qemu_...@crudebyte.com> > --- > fsdev/file-op-9p.h | 1 + > fsdev/qemu-fsdev-opts.c | 7 +++- > fsdev/qemu-fsdev.c | 6 +++ > hw/9pfs/9p.c | 105 > ++++++++++++++++++++++++++++++++++++++++++------ > hw/9pfs/9p.h | 12 ++++++ > qemu-options.hx | 17 +++++++- > vl.c | 3 ++ > 7 files changed, 135 insertions(+), 16 deletions(-) > > diff --git a/fsdev/file-op-9p.h b/fsdev/file-op-9p.h > index c757c8099f..6c1663c252 100644 > --- a/fsdev/file-op-9p.h > +++ b/fsdev/file-op-9p.h > @@ -59,6 +59,7 @@ typedef struct ExtendedOps { > #define V9FS_RDONLY 0x00000040 > #define V9FS_PROXY_SOCK_FD 0x00000080 > #define V9FS_PROXY_SOCK_NAME 0x00000100 > +#define V9FS_REMAP_INODES 0x00000200 > > #define V9FS_SEC_MASK 0x0000003C > > diff --git a/fsdev/qemu-fsdev-opts.c b/fsdev/qemu-fsdev-opts.c > index 7c31ffffaf..64a8052266 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 = "remap_inodes", > + .type = QEMU_OPT_BOOL, > }, { > .name = "socket", > .type = QEMU_OPT_STRING, > @@ -76,6 +78,9 @@ static QemuOptsList qemu_virtfs_opts = { > .name = "readonly", > .type = QEMU_OPT_BOOL, > }, { > + .name = "remap_inodes", > + .type = QEMU_OPT_BOOL, > + }, { > .name = "socket", > .type = QEMU_OPT_STRING, > }, { > diff --git a/fsdev/qemu-fsdev.c b/fsdev/qemu-fsdev.c > index 077a8c4e2b..b6fa9799be 100644 > --- a/fsdev/qemu-fsdev.c > +++ b/fsdev/qemu-fsdev.c > @@ -121,6 +121,7 @@ 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"); > + bool remap_inodes = qemu_opt_get_bool(opts, "remap_inodes", 0); > bool ro = qemu_opt_get_bool(opts, "readonly", 0); > > if (!fsdev_id) { > @@ -161,6 +162,11 @@ int qemu_fsdev_add(QemuOpts *opts, Error **errp) > } else { > fsle->fse.export_flags &= ~V9FS_RDONLY; > } > + if (remap_inodes) { > + fsle->fse.export_flags |= V9FS_REMAP_INODES; > + } else { > + fsle->fse.export_flags &= ~V9FS_REMAP_INODES; > + } > > 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 cbaa212625..7ccc68a829 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; > @@ -571,24 +572,96 @@ 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 */ And we won't ever be able to allocate a new one. Maybe worth adding an error_report_once() to inform the user ? > + 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) > { > - size_t size; > + int err; > > - if (pdu->s->dev_id == 0) { > - pdu->s->dev_id = stbuf->st_dev; > - } else 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 -ENOSYS; > + 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 == 0) { > + pdu->s->dev_id = stbuf->st_dev; > + } else if (pdu->s->dev_id != stbuf->st_dev) { > + error_report_once( > + "9p: Multiple devices detected in same VirtFS export. " > + "You must either use a separate export for each device " > + "shared from host or enable virtfs option 'remap_inodes'." > + ); > + return -ENOSYS; > + } > + size_t size; From CODING_STYLE: 5. Declarations Mixed declarations (interleaving statements and declarations within blocks) are generally not allowed; declarations should be at the beginning of blocks. Please do so for "size" and add an extra blank line. > + 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)) { > @@ -3676,6 +3749,10 @@ int v9fs_device_realize_common(V9fsState *s, const > V9fsTransport *t, > > s->dev_id = 0; > > + /* 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); > > @@ -3689,6 +3766,7 @@ out: > } > g_free(s->tag); > g_free(s->ctx.fs_root); > + qpp_table_destroy(&s->qpp_table); > v9fs_path_free(&path); > } > return rc; > @@ -3701,6 +3779,7 @@ 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..0200e04176 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 (((unsigned long)1 << 48) - 1) This won't give the expected result on a 32-bit host. Since this is a mask for 64-bit entities, it should rather be: #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; > @@ -257,6 +267,8 @@ struct V9fsState > V9fsConf fsconf; > V9fsQID root_qid; > 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 0d8beb4afd..e7ea136da1 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -1334,7 +1334,7 @@ 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" > + " > [,id=id][,writeout=immediate][,readonly][,fmode=fmode][,dmode=dmode][,remap_inodes]\n" This feature applies to all backends IIUC. We don't really care for the synth backend since it generates non-colliding inode numbers by design, but the proxy backend has the same issue as local. So... > "-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" ... please update these two ^^ as well. > "-virtfs synth,mount_tag=tag[,id=id][,readonly]\n", > @@ -1342,7 +1342,7 @@ DEF("virtfs", HAS_ARG, QEMU_OPTION_virtfs, > > 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}] > +@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}][,remap_inodes] > @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] Ditto. > @itemx -virtfs synth,mount_tag=@var{mount_tag} > @@ -1398,6 +1398,19 @@ 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 remap_inodes > +By default virtfs 9p supports only one device per export in order to avoid > +file ID collisions on guest which may otherwise happen because the original > +device IDs from host are not passed and exposed on guest. Instead all files > +of an export shared with virtfs do have 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. For that reason it is recommended to create a > +separate virtfs export for each device to be shared with guests. However > +you may also enable "remap_inodes" 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. > @end table > ETEXI > > diff --git a/vl.c b/vl.c > index 99a56b5556..de9d7b846c 100644 > --- a/vl.c > +++ b/vl.c > @@ -3457,6 +3457,9 @@ int main(int argc, char **argv, char **envp) > qemu_opt_set_bool(fsdev, "readonly", > qemu_opt_get_bool(opts, "readonly", 0), > &error_abort); > + qemu_opt_set_bool(fsdev, "remap_inodes", > + qemu_opt_get_bool(opts, "remap_inodes", 0), > + &error_abort); > device = qemu_opts_create(qemu_find_opts("device"), NULL, 0, > &error_abort); > qemu_opt_set(device, "driver", "virtio-9p-pci", > &error_abort);