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[xen master] tools/xenstore: rework struct xs_tdb_record_hdr



commit 45ce0cb38f7ae0f2d0a2694af85a253524d97f87
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Mon Aug 14 09:46:57 2023 +0200
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Fri Aug 18 13:44:48 2023 +0100

    tools/xenstore: rework struct xs_tdb_record_hdr
    
    Struct xs_tdb_record_hdr is used for nodes stored in the data base.
    When working on a node, struct node is being used, which is including
    the same information as struct xs_tdb_record_hdr, but in a different
    format. Rework struct xs_tdb_record_hdr in order to prepare including
    it in struct node.
    
    Do the following modifications:
    
    - move its definition to xenstored_core.h, as the reason to put it into
      utils.h are no longer existing
    
    - rename it to struct node_hdr, as the "tdb" in its name has only
      historical reasons
    
    - replace the empty permission array at the end with a comment about
      the layout of data in the data base (concatenation of header,
      permissions, node contents, and children list)
    
    - use narrower types for num_perms and datalen, as those are naturally
      limited to XENSTORE_PAYLOAD_MAX (childlen is different here, as it is
      in theory basically unlimited)
    
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
---
 tools/xenstore/utils.h                 |  9 -------
 tools/xenstore/xenstored_core.c        | 46 +++++++++++++++++++++++-----------
 tools/xenstore/xenstored_core.h        | 20 ++++++++++++++-
 tools/xenstore/xenstored_transaction.c |  6 ++---
 4 files changed, 53 insertions(+), 28 deletions(-)

diff --git a/tools/xenstore/utils.h b/tools/xenstore/utils.h
index 028ecb9d7a..405d662ea2 100644
--- a/tools/xenstore/utils.h
+++ b/tools/xenstore/utils.h
@@ -9,15 +9,6 @@
 
 #include "xenstore_lib.h"
 
-/* Header of the node record in tdb. */
-struct xs_tdb_record_hdr {
-       uint64_t generation;
-       uint32_t num_perms;
-       uint32_t datalen;
-       uint32_t childlen;
-       struct xs_permissions perms[0];
-};
-
 /* Is A == B ? */
 #define streq(a,b) (strcmp((a),(b)) == 0)
 
diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 53e29aeb9a..9fc17a9efc 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -555,9 +555,9 @@ static void initialize_fds(int *p_sock_pollfd_idx, int 
*ptimeout)
        }
 }
 
-const struct xs_tdb_record_hdr *db_fetch(const char *db_name, size_t *size)
+const struct node_hdr *db_fetch(const char *db_name, size_t *size)
 {
-       const struct xs_tdb_record_hdr *hdr;
+       const struct node_hdr *hdr;
 
        hdr = hashtable_search(nodes, db_name);
        if (!hdr) {
@@ -565,7 +565,7 @@ const struct xs_tdb_record_hdr *db_fetch(const char 
*db_name, size_t *size)
                return NULL;
        }
 
-       *size = sizeof(*hdr) + hdr->num_perms * sizeof(hdr->perms[0]) +
+       *size = sizeof(*hdr) + hdr->num_perms * sizeof(struct xs_permissions) +
                hdr->datalen + hdr->childlen;
 
        trace_tdb("read %s size %zu\n", db_name, *size + strlen(db_name));
@@ -573,10 +573,16 @@ const struct xs_tdb_record_hdr *db_fetch(const char 
*db_name, size_t *size)
        return hdr;
 }
 
+static const struct xs_permissions *perms_from_node_hdr(
+       const struct node_hdr *hdr)
+{
+       return (const struct xs_permissions *)(hdr + 1);
+}
+
 static void get_acc_data(const char *name, struct node_account_data *acc)
 {
        size_t size;
-       const struct xs_tdb_record_hdr *hdr;
+       const struct node_hdr *hdr;
 
        if (acc->memory < 0) {
                hdr = db_fetch(name, &size);
@@ -585,7 +591,7 @@ static void get_acc_data(const char *name, struct 
node_account_data *acc)
                        acc->memory = 0;
                } else {
                        acc->memory = size;
-                       acc->domid = hdr->perms[0].id;
+                       acc->domid = perms_from_node_hdr(hdr)->id;
                }
        }
 }
@@ -606,7 +612,7 @@ int db_write(struct connection *conn, const char *db_name, 
void *data,
             size_t size, struct node_account_data *acc,
             enum write_node_mode mode, bool no_quota_check)
 {
-       struct xs_tdb_record_hdr *hdr = data;
+       const struct node_hdr *hdr = data;
        struct node_account_data old_acc = {};
        unsigned int old_domid, new_domid;
        size_t name_len = strlen(db_name);
@@ -620,7 +626,7 @@ int db_write(struct connection *conn, const char *db_name, 
void *data,
 
        get_acc_data(db_name, &old_acc);
        old_domid = get_acc_domid(conn, db_name, old_acc.domid);
-       new_domid = get_acc_domid(conn, db_name, hdr->perms[0].id);
+       new_domid = get_acc_domid(conn, db_name, perms_from_node_hdr(hdr)->id);
 
        /*
         * Don't check for ENOENT, as we want to be able to switch orphaned
@@ -661,7 +667,7 @@ int db_write(struct connection *conn, const char *db_name, 
void *data,
 
        if (acc) {
                /* Don't use new_domid, as it might be a transaction node. */
-               acc->domid = hdr->perms[0].id;
+               acc->domid = perms_from_node_hdr(hdr)->id;
                acc->memory = size;
        }
 
@@ -699,7 +705,7 @@ struct node *read_node(struct connection *conn, const void 
*ctx,
                       const char *name)
 {
        size_t size;
-       const struct xs_tdb_record_hdr *hdr;
+       const struct node_hdr *hdr;
        struct node *node;
        const char *db_name;
        int err;
@@ -733,12 +739,12 @@ struct node *read_node(struct connection *conn, const 
void *ctx,
        node->perms.num = hdr->num_perms;
        node->datalen = hdr->datalen;
        node->childlen = hdr->childlen;
-       node->acc.domid = hdr->perms[0].id;
+       node->acc.domid = perms_from_node_hdr(hdr)->id;
        node->acc.memory = size;
 
        /* Copy node data to new memory area, starting with permissions. */
        size -= sizeof(*hdr);
-       node->perms.p = talloc_memdup(node, hdr->perms, size);
+       node->perms.p = talloc_memdup(node, perms_from_node_hdr(hdr), size);
        if (node->perms.p == NULL) {
                errno = ENOMEM;
                goto error;
@@ -785,7 +791,7 @@ int write_node_raw(struct connection *conn, const char 
*db_name,
        void *data;
        size_t size;
        void *p;
-       struct xs_tdb_record_hdr *hdr;
+       struct node_hdr *hdr;
 
        if (domain_adjust_node_perms(node))
                return errno;
@@ -806,15 +812,18 @@ int write_node_raw(struct connection *conn, const char 
*db_name,
                return errno;
        }
 
+       BUILD_BUG_ON(XENSTORE_PAYLOAD_MAX >= (typeof(hdr->datalen))(-1));
+
        hdr = data;
        hdr->generation = node->generation;
        hdr->num_perms = node->perms.num;
        hdr->datalen = node->datalen;
        hdr->childlen = node->childlen;
 
-       memcpy(hdr->perms, node->perms.p,
-              node->perms.num * sizeof(*node->perms.p));
-       p = hdr->perms + node->perms.num;
+       /* Open code perms_from_node_hdr() for the non-const case. */
+       p = hdr + 1;
+       memcpy(p, node->perms.p, node->perms.num * sizeof(*node->perms.p));
+       p += node->perms.num * sizeof(*node->perms.p);
        memcpy(p, node->data, node->datalen);
        p += node->datalen;
        memcpy(p, node->children, node->childlen);
@@ -2144,6 +2153,13 @@ static void handle_input(struct connection *conn)
                        if (in->used != sizeof(in->hdr))
                                return;
 
+                       /*
+                        * The payload size is not only currently restricted by
+                        * the protocol but also the internal implementation
+                        * (see various BUILD_BUG_ON()).
+                        * Any potential change of the maximum payload size
+                        * needs to be negotiated between the involved parties.
+                        */
                        if (in->hdr.msg.len > XENSTORE_PAYLOAD_MAX) {
                                syslog(LOG_ERR, "Client tried to feed us %i",
                                       in->hdr.msg.len);
diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.h
index 4a370f766f..1a933892e3 100644
--- a/tools/xenstore/xenstored_core.h
+++ b/tools/xenstore/xenstored_core.h
@@ -168,6 +168,24 @@ struct connection
 };
 extern struct list_head connections;
 
+/*
+ * Header of the node record in the data base.
+ * In the data base the memory of the node is a single memory chunk with the
+ * following format:
+ * struct {
+ *     node_hdr hdr;
+ *     struct xs_permissions perms[hdr.num_perms];
+ *     char data[hdr.datalen];
+ *     char children[hdr.childlen];
+ * };
+ */
+struct node_hdr {
+       uint64_t generation;
+       uint16_t num_perms;
+       uint16_t datalen;
+       uint32_t childlen;
+};
+
 struct node_perms {
        unsigned int num;
        struct xs_permissions *p;
@@ -362,7 +380,7 @@ extern xengnttab_handle **xgt_handle;
 int remember_string(struct hashtable *hash, const char *str);
 
 /* Data base access functions. */
-const struct xs_tdb_record_hdr *db_fetch(const char *db_name, size_t *size);
+const struct node_hdr *db_fetch(const char *db_name, size_t *size);
 int db_write(struct connection *conn, const char *db_name, void *data,
             size_t size, struct node_account_data *acc,
             enum write_node_mode mode, bool no_quota_check);
diff --git a/tools/xenstore/xenstored_transaction.c 
b/tools/xenstore/xenstored_transaction.c
index a90283dcc5..9ca73b9874 100644
--- a/tools/xenstore/xenstored_transaction.c
+++ b/tools/xenstore/xenstored_transaction.c
@@ -357,7 +357,7 @@ static int finalize_transaction(struct connection *conn,
 {
        struct accessed_node *i, *n;
        size_t size;
-       const struct xs_tdb_record_hdr *hdr;
+       const struct node_hdr *hdr;
        uint64_t gen;
 
        list_for_each_entry_safe(i, n, &trans->accessed, list) {
@@ -394,12 +394,12 @@ static int finalize_transaction(struct connection *conn,
                                 * generation count.
                                 */
                                enum write_node_mode mode;
-                               struct xs_tdb_record_hdr *own;
+                               struct node_hdr *own;
 
                                talloc_increase_ref_count(hdr);
                                db_delete(conn, i->trans_name, NULL);
 
-                               own = (struct xs_tdb_record_hdr *)hdr;
+                               own = (struct node_hdr *)hdr;
                                own->generation = ++generation;
                                mode = (i->generation == NO_GENERATION)
                                       ? NODE_CREATE : NODE_MODIFY;
--
generated by git-patchbot for /home/xen/git/xen.git#master



 


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