value strings: pretty printers for flags and enums

This adds zfs_valstr, a collection of pretty printers for bitfields and
enums. These are useful in debugging, logging and other display contexts
where raw values are difficult for the untrained (or even trained!) eye
to decipher.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>

include/Makefile.am

@@ -14,6 +14,7 @@ COMMON_H = \
 	zfs_fletcher.h \
 	zfs_namecheck.h \
 	zfs_prop.h \
+	zfs_valstr.h \
 	\
 	sys/abd.h \
 	sys/abd_impl.h \

include/sys/zio.h

@@ -167,6 +167,9 @@ typedef enum zio_suspend_reason {
  * This was originally an enum type. However, those are 32-bit and there is no
  * way to make a 64-bit enum type. Since we ran out of bits for flags, we were
  * forced to upgrade it to a uint64_t.
+ *
+ * NOTE: PLEASE UPDATE THE BITFIELD STRINGS IN zfs_valstr.c IF YOU ADD ANOTHER
+ * FLAG.
  */
 typedef uint64_t zio_flag_t;
 	/*

include/sys/zio_impl.h

@@ -120,6 +120,9 @@ extern "C" {
 
 /*
  * zio pipeline stage definitions
+ *
+ * NOTE: PLEASE UPDATE THE BITFIELD STRINGS IN zfs_valstr.c IF YOU ADD ANOTHER
+ * FLAG.
  */
 enum zio_stage {
 	ZIO_STAGE_OPEN			= 1 << 0,	/* RWFCXT */

include/sys/zio_priority.h

@@ -22,6 +22,10 @@
 extern "C" {
 #endif
 
+/*
+ * NOTE: PLEASE UPDATE THE ENUM STRINGS IN zfs_valstr.c IF YOU ADD ANOTHER
+ * VALUE.
+ */
 typedef enum zio_priority {
 	ZIO_PRIORITY_SYNC_READ,
 	ZIO_PRIORITY_SYNC_WRITE,	/* ZIL */

include/zfs_valstr.h

@@ -0,0 +1,84 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or https://opensource.org/licenses/CDDL-1.0.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2024, Klara Inc.
+ */
+
+#ifndef	_ZFS_VALSTR_H
+#define	_ZFS_VALSTR_H extern __attribute__((visibility("default")))
+
+#include <sys/fs/zfs.h>
+#include <sys/types.h>
+
+#ifdef	__cplusplus
+extern "C" {
+#endif
+
+/*
+ * These macros create function prototypes for pretty-printing or stringifying
+ * certain kinds of numeric types.
+ *
+ * _ZFS_VALSTR_DECLARE_BITFIELD(name) creates:
+ *
+ *   size_t zfs_valstr_<name>_bits(uint64_t bits, char *out, size_t outlen);
+ *     expands single char for each set bit, and space for each clear bit
+ *
+ *   size_t zfs_valstr_<name>_pairs(uint64_t bits, char *out, size_t outlen);
+ *     expands two-char mnemonic for each bit set in `bits`, separated by `|`
+ *
+ *   size_t zfs_valstr_<name>(uint64_t bits, char *out, size_t outlen);
+ *     expands full name of each bit set in `bits`, separated by spaces
+ *
+ * _ZFS_VALSTR_DECLARE_ENUM(name) creates:
+ *
+ *   size_t zfs_valstr_<name>(int v, char *out, size_t outlen);
+ *     expands full name of enum value
+ *
+ * Each _ZFS_VALSTR_DECLARE_xxx needs a corresponding _VALSTR_xxx_IMPL string
+ * table in vfs_valstr.c.
+ */
+
+#define	_ZFS_VALSTR_DECLARE_BITFIELD(name)			\
+	_ZFS_VALSTR_H size_t zfs_valstr_ ## name ## _bits(	\
+	    uint64_t bits, char *out, size_t outlen);		\
+	_ZFS_VALSTR_H size_t zfs_valstr_ ## name ## _pairs(	\
+	    uint64_t bits, char *out, size_t outlen);		\
+	_ZFS_VALSTR_H size_t zfs_valstr_ ## name(		\
+	    uint64_t bits, char *out, size_t outlen);		\
+
+#define	_ZFS_VALSTR_DECLARE_ENUM(name)				\
+	_ZFS_VALSTR_H size_t zfs_valstr_ ## name(		\
+	    int v, char *out, size_t outlen);			\
+
+_ZFS_VALSTR_DECLARE_BITFIELD(zio_flag)
+_ZFS_VALSTR_DECLARE_BITFIELD(zio_stage)
+
+_ZFS_VALSTR_DECLARE_ENUM(zio_priority)
+
+#undef _ZFS_VALSTR_DECLARE_BITFIELD
+#undef _ZFS_VALSTR_DECLARE_ENUM
+
+#ifdef	__cplusplus
+}
+#endif
+
+#endif	/* _ZFS_VALSTR_H */