Add zap_prefetch() interface

Provide a generic interface to prefetch ZAP entries by name.  This
functionality is being added for external consumers such as Lustre.
It is based of the existing zap_prefetch_uint64() version which is
used by the deduplication code.

Signed-off-by: Brian Behlendorf <[email protected]>
Signed-off-by: Richard Yao <[email protected]>
Closes #4061

2 files changed, 24 insertions, 0 deletions

diff --git a/include/sys/zap.h b/include/sys/zap.h
index bc15237bf..ed60b86db 100644
--- a/include/sys/zap.h
+++ b/include/sys/zap.h
@@ -213,6 +213,7 @@ int zap_lookup_norm(objset_t *ds, uint64_t zapobj, const char *name,
 int zap_lookup_uint64(objset_t *os, uint64_t zapobj, const uint64_t *key,
     int key_numints, uint64_t integer_size, uint64_t num_integers, void *buf);
 int zap_contains(objset_t *ds, uint64_t zapobj, const char *name);
+int zap_prefetch(objset_t *os, uint64_t zapobj, const char *name);
 int zap_prefetch_uint64(objset_t *os, uint64_t zapobj, const uint64_t *key,
     int key_numints);
 
diff --git a/module/zfs/zap_micro.c b/module/zfs/zap_micro.c
index 29406e660..85b465b05 100644
--- a/module/zfs/zap_micro.c
+++ b/module/zfs/zap_micro.c
@@ -814,6 +814,28 @@ zap_lookup_norm(objset_t *os, uint64_t zapobj, const char *name,
 }
 
 int
+zap_prefetch(objset_t *os, uint64_t zapobj, const char *name)
+{
+	zap_t *zap;
+	int err;
+	zap_name_t *zn;
+
+	err = zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, &zap);
+	if (err)
+		return (err);
+	zn = zap_name_alloc(zap, name, MT_EXACT);
+	if (zn == NULL) {
+		zap_unlockdir(zap);
+		return (SET_ERROR(ENOTSUP));
+	}
+
+	fzap_prefetch(zn);
+	zap_name_free(zn);
+	zap_unlockdir(zap);
+	return (err);
+}
+
+int
 zap_prefetch_uint64(objset_t *os, uint64_t zapobj, const uint64_t *key,
     int key_numints)
 {
@@ -1427,6 +1449,7 @@ EXPORT_SYMBOL(zap_lookup);
 EXPORT_SYMBOL(zap_lookup_norm);
 EXPORT_SYMBOL(zap_lookup_uint64);
 EXPORT_SYMBOL(zap_contains);
+EXPORT_SYMBOL(zap_prefetch);
 EXPORT_SYMBOL(zap_prefetch_uint64);
 EXPORT_SYMBOL(zap_count_write);
 EXPORT_SYMBOL(zap_add);