Commit f3fe4a2d authored by Antonios Motakis's avatar Antonios Motakis Committed by Greg Kurz
Browse files

9p: stat_to_qid: implement slow path 



stat_to_qid attempts via qid_path_prefixmap to map unique files (which are
identified by 64 bit inode nr and 32 bit device id) to a 64 QID path value.
However this implementation makes some assumptions about inode number
generation on the host.

If qid_path_prefixmap fails, we still have 48 bits available in the QID
path to fall back to a less memory efficient full mapping.

Signed-off-by: default avatarAntonios Motakis <antonios.motakis@huawei.com>
[CS: - Rebased to https://github.com/gkurz/qemu/commits/9p-next


       (SHA1 7fc4c49e91).
     - Updated hash calls to new xxhash API.
     - Removed unnecessary parantheses in qpf_lookup_func().
     - Removed unnecessary g_malloc0() result checks.
     - Log error message when running out of prefixes in
       qid_path_fullmap().
     - Log warning message about potential degraded performance in
       qid_path_prefixmap().
     - Wrapped qpf_table initialization to dedicated qpf_table_init()
       function.
     - Fixed typo in comment. ]
Signed-off-by: default avatarChristian Schoenebeck <qemu_oss@crudebyte.com>
Signed-off-by: default avatarGreg Kurz <groug@kaod.org>
parent 1a6ed33c

hw/9pfs/9p.c

+67 −7
Original line number Diff line number Diff line
@@ -579,23 +579,34 @@ static uint32_t qpp_hash(QppEntry e) 
    return qemu_xxhash7(e.ino_prefix, e.dev, 0, 0, 0);

}



static uint32_t qpf_hash(QpfEntry e)

{

    return qemu_xxhash7(e.ino, 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)

static bool qpf_lookup_func(const void *obj, const void *userp)

{

    const QpfEntry *e1 = obj, *e2 = userp;

    return e1->dev == e2->dev && e1->ino == e2->ino;

}



static void qp_table_remove(void *p, uint32_t h, void *up)

{

    g_free(p);

}



static void qpp_table_destroy(struct qht *ht)

static void qp_table_destroy(struct qht *ht)

{

    if (!ht || !ht->map) {

        return;

    }

    qht_iter(ht, qpp_table_remove, NULL);

    qht_iter(ht, qp_table_remove, NULL);

    qht_destroy(ht);

}
@@ -604,6 +615,50 @@ static void qpp_table_init(struct qht *ht) 
    qht_init(ht, qpp_lookup_func, 1, QHT_MODE_AUTO_RESIZE);

}



static void qpf_table_init(struct qht *ht)

{

    qht_init(ht, qpf_lookup_func, 1 << 16, QHT_MODE_AUTO_RESIZE);

}



static int qid_path_fullmap(V9fsPDU *pdu, const struct stat *stbuf,

                            uint64_t *path)

{

    QpfEntry lookup = {

        .dev = stbuf->st_dev,

        .ino = stbuf->st_ino

    }, *val;

    uint32_t hash = qpf_hash(lookup);



    /* most users won't need the fullmap, so init the table lazily */

    if (!pdu->s->qpf_table.map) {

        qpf_table_init(&pdu->s->qpf_table);

    }



    val = qht_lookup(&pdu->s->qpf_table, &lookup, hash);



    if (!val) {

        if (pdu->s->qp_fullpath_next == 0) {

            /* no more files can be mapped :'( */

            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 and device combo */

        val->path = pdu->s->qp_fullpath_next++;

        pdu->s->qp_fullpath_next &= QPATH_INO_MASK;

        qht_insert(&pdu->s->qpf_table, val, hash, NULL);

    }



    *path = val->path;

    return 0;

}



/*

 * 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
@@ -629,9 +684,8 @@ static int qid_path_prefixmap(V9fsPDU *pdu, const struct stat *stbuf, 
    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."

            warn_report_once(

                "9p: Potential degraded performance of inode remapping"

            );

            return -ENFILE;

        }
@@ -656,6 +710,10 @@ static int stat_to_qid(V9fsPDU *pdu, const struct stat *stbuf, V9fsQID *qidp) 
    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 == -ENFILE) {

            /* fast path didn't work, fall back to full map */

            err = qid_path_fullmap(pdu, stbuf, &qidp->path);

        }

        if (err) {

            return err;

        }
@@ -3820,6 +3878,7 @@ int v9fs_device_realize_common(V9fsState *s, const V9fsTransport *t, 


    qpp_table_init(&s->qpp_table);

    s->qp_prefix_next = 1; /* reserve 0 to detect overflow */

    s->qp_fullpath_next = 1;



    s->ctx.fst = &fse->fst;

    fsdev_throttle_init(s->ctx.fst);
@@ -3842,7 +3901,8 @@ 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);

    qp_table_destroy(&s->qpp_table);

    qp_table_destroy(&s->qpf_table);

    g_free(s->ctx.fs_root);

}

hw/9pfs/9p.h

+9 −0
Original line number Diff line number Diff line
@@ -245,6 +245,13 @@ typedef struct { 
    uint16_t qp_prefix;

} QppEntry;



/* QID path full entry, as above */

typedef struct {

    dev_t dev;

    ino_t ino;

    uint64_t path;

} QpfEntry;



struct V9fsState

{

    QLIST_HEAD(, V9fsPDU) free_list;
@@ -268,7 +275,9 @@ struct V9fsState 
    V9fsQID root_qid;

    dev_t dev_id;

    struct qht qpp_table;

    struct qht qpf_table;

    uint16_t qp_prefix_next;

    uint64_t qp_fullpath_next;

};



/* 9p2000.L open flags */