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Re: [PATCH 10/11] tools/xenstore: drop use of tdb
On 20.06.23 15:09, Julien Grall wrote:
Hi Juergen,
On 30/05/2023 10:13, Juergen Gross wrote:
Today all Xenstore nodes are stored in a TDB data base. This data base
has several disadvantages:
- it is using a fixed sized hash table, resulting in high memory
overhead for small installations with only very few VMs, and a rather
large performance hit for systems with lots of VMs due to many
collisions
- Xenstore is only single-threaded, while TDB is designed to be fit
for multi-threaded use cases, resulting in much higher code
complexity than needed
- special use cases of Xenstore are not possible to implement with TDB
in an effective way, while an implementation of a data base tailored
for Xenstore could simplify some handling (e.g. transactions) a lot
So drop using TDB and store the nodes directly in memory making them
easily accessible. Use a hash-based lookup mechanism for fast lookup
of nodes by their full path.
For now only replace TDB keeping the current access functions.
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
tools/xenstore/xenstored_core.c | 153 ++++++++++---------------
tools/xenstore/xenstored_core.h | 5 +-
tools/xenstore/xenstored_transaction.c | 1 -
3 files changed, 62 insertions(+), 97 deletions(-)
diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 12c584f09b..9b44de9d31 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -53,7 +53,6 @@
#include "xenstored_domain.h"
#include "xenstored_control.h"
#include "xenstored_lu.h"
-#include "tdb.h"
#ifndef NO_SOCKETS
#if defined(HAVE_SYSTEMD)
@@ -85,7 +84,7 @@ bool keep_orphans = false;
static int reopen_log_pipe[2];
static int reopen_log_pipe0_pollfd_idx = -1;
char *tracefile = NULL;
-static TDB_CONTEXT *tdb_ctx = NULL;
+static struct hashtable *nodes;
unsigned int trace_flags = TRACE_OBJ | TRACE_IO;
static const char *sockmsg_string(enum xsd_sockmsg_type type);
@@ -556,28 +555,29 @@ static void initialize_fds(int *p_sock_pollfd_idx, int
*ptimeout)
}
}
-static void set_tdb_key(const char *name, TDB_DATA *key)
-{
- /*
- * Dropping const is fine here, as the key will never be modified
- * by TDB.
- */
- key->dptr = (char *)name;
- key->dsize = strlen(name);
-}
-
void *db_fetch(const char *db_name, size_t *size)
{
- TDB_DATA key, data;
+ struct xs_tdb_record_hdr *hdr;
AFAICT, this could be const.
Yes.
+ void *p;
p will point to xs_tdb_record_hdr, right? If so, I think it should be
xs_tdb_record_hdr.
I agree.
- set_tdb_key(db_name, &key);
- data = tdb_fetch(tdb_ctx, key);
- if (!data.dptr)
- errno = (tdb_error(tdb_ctx) == TDB_ERR_NOEXIST) ? ENOENT : EIO;
- else
- *size = data.dsize;
+ hdr = hashtable_search(nodes, db_name);
+ if (!hdr) {
+ errno = ENOENT;
+ return NULL;
+ }
+
+ *size = sizeof(*hdr) + hdr->num_perms * sizeof(hdr->perms[0]) +
+ hdr->datalen + hdr->childlen;
AFAICT, this is the same computation as in write_node_raw. Can we introduce a
wrapper for it?
Okay.
+
+ p = talloc_size(NULL, *size);
+ if (!p) {
+ errno = ENOMEM;
+ return NULL;
+ }
- return data.dptr;
+ memcpy(p, hdr, *size);
It would be a good opportunity to explain the reasoning behind returning a fresh
value rather than a pointer on the DB entry.
I'll add a comment.
+
+ return p;
}
static void get_acc_data(const char *name, struct node_account_data *acc)
@@ -621,12 +621,10 @@ int db_write(struct connection *conn, const char
*db_name, void *data,
struct xs_tdb_record_hdr *hdr = data;
struct node_account_data old_acc = {};
unsigned int old_domid, new_domid;
+ size_t name_len = strlen(db_name);
+ const char *name;
int ret;
- TDB_DATA key, dat;
- set_tdb_key(db_name, &key);
- dat.dptr = data;
- dat.dsize = size;
if (!acc)
old_acc.memory = -1;
else
@@ -642,29 +640,36 @@ int db_write(struct connection *conn, const char
*db_name, void *data,
*/
if (old_acc.memory)
domain_memory_add_nochk(conn, old_domid,
- -old_acc.memory - key.dsize);
- ret = domain_memory_add(conn, new_domid, size + key.dsize,
+ -old_acc.memory - name_len);
+ ret = domain_memory_add(conn, new_domid, size + name_len,
no_quota_check);
if (ret) {
/* Error path, so no quota check. */
if (old_acc.memory)
domain_memory_add_nochk(conn, old_domid,
- old_acc.memory + key.dsize);
+ old_acc.memory + name_len);
return ret;
}
- /* TDB should set errno, but doesn't even set ecode AFAICT. */
- if (tdb_store(tdb_ctx, key, dat,
- (flag == NODE_CREATE) ? TDB_INSERT : TDB_MODIFY) != 0) {
- domain_memory_add_nochk(conn, new_domid, -size - key.dsize);
+ if (flag == NODE_CREATE) {
+ /* db_name could be modified later, so allocate a copy. */
+ name = talloc_strdup(data, db_name);
+ ret = name ? hashtable_add(nodes, name, data) : ENOMEM;
+ } else
+ ret = hashtable_replace(nodes, db_name, data);
+
+ if (ret) {
+ /* Free data, as it isn't owned by hashtable now. */
+ talloc_free(data);
+ domain_memory_add_nochk(conn, new_domid, -size - name_len);
/* Error path, so no quota check. */
if (old_acc.memory)
domain_memory_add_nochk(conn, old_domid,
- old_acc.memory + key.dsize);
- errno = EIO;
+ old_acc.memory + name_len);
+ errno = ret;
return errno;
}
- trace_tdb("store %s size %zu\n", db_name, size + key.dsize);
+ trace_tdb("store %s size %zu\n", db_name, size + name_len);
if (acc) {
/* Don't use new_domid, as it might be a transaction node. */
@@ -680,9 +685,6 @@ int db_delete(struct connection *conn, const char *name,
AFAICT, we will always return 0 after this patch. Do you plan to clean-up the
return type?
Good catch. Will do it in a followup patch.
{
struct node_account_data tmp_acc;
unsigned int domid;
- TDB_DATA key;
-
- set_tdb_key(name, &key);
if (!acc) {
acc = &tmp_acc;
@@ -691,15 +693,13 @@ int db_delete(struct connection *conn, const char *name,
get_acc_data(name, acc);
- if (tdb_delete(tdb_ctx, key)) {
- errno = EIO;
- return errno;
- }
+ hashtable_remove(nodes, name);
trace_tdb("delete %s\n", name);
if (acc->memory) {
domid = get_acc_domid(conn, name, acc->domid);
- domain_memory_add_nochk(conn, domid, -acc->memory - key.dsize);
+ domain_memory_add_nochk(conn, domid,
+ -acc->memory - strlen(name));
}
return 0;
@@ -2352,43 +2352,29 @@ static void manual_node(const char *name, const char
*child)
talloc_free(node);
}
-static void tdb_logger(TDB_CONTEXT *tdb, int level, const char * fmt, ...)
+static unsigned int hash_from_key_fn(const void *k)
{
- va_list ap;
- char *s;
- int saved_errno = errno;
+ const char *str = k;
+ unsigned int hash = 5381;
+ char c;
- va_start(ap, fmt);
- s = talloc_vasprintf(NULL, fmt, ap);
- va_end(ap);
+ while ((c = *str++))
+ hash = ((hash << 5) + hash) + (unsigned int)c;
- if (s) {
- trace("TDB: %s\n", s);
- syslog(LOG_ERR, "TDB: %s", s);
- if (verbose)
- xprintf("TDB: %s", s);
- talloc_free(s);
- } else {
- trace("talloc failure during logging\n");
- syslog(LOG_ERR, "talloc failure during logging\n");
- }
+ return hash;
+}
- errno = saved_errno;
+static int keys_equal_fn(const void *key1, const void *key2)
+{
+ return 0 == strcmp(key1, key2);
}
void setup_structure(bool live_update)
{
- char *tdbname;
-
- tdbname = talloc_strdup(talloc_autofree_context(), "/dev/mem");
- if (!tdbname)
- barf_perror("Could not create tdbname");
-
- tdb_ctx = tdb_open_ex(tdbname, 7919, TDB_INTERNAL | TDB_NOLOCK,
- O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC,
- 0640, &tdb_logger, NULL);
- if (!tdb_ctx)
- barf_perror("Could not create tdb file %s", tdbname);
+ nodes = create_hashtable(NULL, "nodes", hash_from_key_fn, keys_equal_fn,
+ HASHTABLE_FREE_KEY | HASHTABLE_FREE_VALUE);
+ if (!nodes)
+ barf_perror("Could not create nodes hashtable");
if (live_update)
manual_node("/", NULL);
@@ -2402,24 +2388,6 @@ void setup_structure(bool live_update)
}
}
-static unsigned int hash_from_key_fn(const void *k)
-{
- const char *str = k;
- unsigned int hash = 5381;
- char c;
-
- while ((c = *str++))
- hash = ((hash << 5) + hash) + (unsigned int)c;
-
- return hash;
-}
-
-
-static int keys_equal_fn(const void *key1, const void *key2)
-{
- return 0 == strcmp(key1, key2);
-}
-
int remember_string(struct hashtable *hash, const char *str)
{
char *k = talloc_strdup(NULL, str);
@@ -2479,12 +2447,11 @@ static int check_store_enoent(const void *ctx, struct
connection *conn,
/**
* Helper to clean_store below.
*/
-static int clean_store_(TDB_CONTEXT *tdb, TDB_DATA key, TDB_DATA val,
- void *private)
+static int clean_store_(const void *key, void *val, void *private)
{
struct hashtable *reachable = private;
char *slash;
- char * name = talloc_strndup(NULL, key.dptr, key.dsize);
+ char *name = talloc_strdup(NULL, key);
if (!name) {
log("clean_store: ENOMEM");
@@ -2514,7 +2481,7 @@ static int clean_store_(TDB_CONTEXT *tdb, TDB_DATA key,
TDB_DATA val,
*/
static void clean_store(struct check_store_data *data)
{
- tdb_traverse(tdb_ctx, &clean_store_, data->reachable);
+ hashtable_iterate(nodes, clean_store_, data->reachable);
domain_check_acc(data->domains);
}
diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.h
index e922dce775..63c2110135 100644
--- a/tools/xenstore/xenstored_core.h
+++ b/tools/xenstore/xenstored_core.h
@@ -33,7 +33,6 @@
#include "xenstore_lib.h"
#include "xenstore_state.h"
#include "list.h"
-#include "tdb.h"
#include "hashtable.h"
#ifndef O_CLOEXEC
@@ -236,13 +235,13 @@ static inline unsigned int get_node_owner(const struct
node *node)
return node->perms.p[0].id;
}
-/* Write a node to the tdb data base. */
+/* Write a node to the data base. */
int write_node_raw(struct connection *conn, const char *db_name,
struct node *node, int flag, bool no_quota_check);
#define NODE_CREATE 0
#define NODE_MODIFY 1
-/* Get a node from the tdb data base. */
+/* Get a node from the data base. */
struct node *read_node(struct connection *conn, const void *ctx,
const char *name);
diff --git a/tools/xenstore/xenstored_transaction.c
b/tools/xenstore/xenstored_transaction.c
index c51edf432f..21700c2e84 100644
--- a/tools/xenstore/xenstored_transaction.c
+++ b/tools/xenstore/xenstored_transaction.c
@@ -403,7 +403,6 @@ static int finalize_transaction(struct connection *conn,
? NODE_CREATE : NODE_MODIFY;
*is_corrupt |= db_write(conn, i->node, data,
size, NULL, flag, true);
- talloc_free(data);
It is not clear to me why this free was removed.
See db_write(). data is now either owned by the hashtable entry, or it has been
freed in db_write() in the error case.
Juergen
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