btrfs-progs: add musl compatibility for printf format %pV

Glibc provides an interface to extend the printf formats but this is not
standardized and does not work on musl. The code brought from kernel
uses %pV for varargs and also has own implementation of printk.

As a workaround for musl expand the pV value to a string and then
simply print it. The details are hidden behind macros:

- DECLARE_PV(vaf)
- PV_ASSIGN(vaf, format, args)
- PV_FMT in printf string
- PV_VAL in arguments

Signed-off-by: David Sterba <dsterba@suse.com>

common/messages.c

@@ -16,7 +16,6 @@
 
 #include <stdio.h>
 #include <stdarg.h>
-#include <printf.h>
 #include "common/messages.h"
 #include "common/utils.h"
 
@@ -26,8 +25,6 @@ static const char *common_error_string[] = {
 	[ERROR_MSG_COMMIT_TRANS] = "failed to commit transaction",
 };
 
-static int va_modifier = -1;
-
 __attribute__ ((format (printf, 1, 2)))
 void __btrfs_printf(const char *fmt, ...)
 {
@@ -38,6 +35,10 @@ void __btrfs_printf(const char *fmt, ...)
 	va_end(args);
 }
 
+#ifndef PV_WORKAROUND
+
+static int va_modifier = -1;
+
 static int print_va_format(FILE *stream, const struct printf_info *info,
 			   const void *const *args)
 {
@@ -59,17 +60,20 @@ static int print_va_format_arginfo(const struct printf_info *info,
 	}
 	return 1;
 }
+#endif
 
 __attribute__ ((format (printf, 2, 3)))
 void btrfs_no_printk(const void *fs_info, const char *fmt, ...)
 {
 	va_list args;
 
+#ifndef PV_WORKAROUND
 	if (va_modifier == -1) {
 		register_printf_specifier('V', print_va_format,
 					  print_va_format_arginfo);
 		va_modifier = register_printf_modifier(L"p");
 	}
+#endif
 
 	va_start(args, fmt);
 	vfprintf(stderr, fmt, args);

common/messages.h

@@ -22,6 +22,23 @@
 #include <stdio.h>
 #include <errno.h>
 
+/*
+ * Workaround for custom format %pV that may not be supported on all libcs.
+ */
+#ifdef HAVE_PRINTF_H
+#define DECLARE_PV(name)		struct va_format name
+#define PV_FMT				"%pV"
+#define PV_VAL(va)			&va
+#define PV_ASSIGN(_va, _fmt, _args)	({ _va.fmt = (_fmt); _va.va = &(_args); })
+#include <printf.h>
+#else
+#define PV_WORKAROUND
+#define DECLARE_PV(name)		char name[1024]
+#define PV_FMT				"%s"
+#define PV_VAL(va)			va
+#define PV_ASSIGN(_va, _fmt, _args)	vsnprintf(_va, 1024, _fmt, _args)
+#endif
+
 #ifdef DEBUG_VERBOSE_ERROR
 #define	PRINT_VERBOSE_ERROR	fprintf(stderr, "%s:%d:", __FILE__, __LINE__)
 #else

configure.ac

@@ -85,6 +85,7 @@ AX_GCC_BUILTIN([__builtin_mul_overflow])
 AC_CHECK_HEADERS([linux/perf_event.h])
 AC_CHECK_HEADERS([linux/hw_breakpoint.h])
 AC_CHECK_HEADERS([linux/fsverity.h])
+AC_CHECK_HEADERS([printf.h])
 
 if grep -q 'HAVE_LINUX_FSVERITY_H.*1' confdefs.h; then
 	have_fsverity='yes'

kernel-shared/messages.c

@@ -134,15 +134,14 @@ void __btrfs_handle_fs_error(struct btrfs_fs_info *fs_info, const char *function
 	errstr = btrfs_decode_error(error);
 	btrfs_state_to_string(fs_info, statestr);
 	if (fmt) {
-		struct va_format vaf;
+		DECLARE_PV(vaf);
 		va_list args;
 
 		va_start(args, fmt);
-		vaf.fmt = fmt;
+		PV_ASSIGN(vaf, fmt, args);
-		vaf.va = &args;
 
-		pr_crit("BTRFS: error (device %s%s) in %s:%d: error=%d %s (%pV)\n",
+		pr_crit("BTRFS: error (device %s%s) in %s:%d: error=%d %s (" PV_FMT ")\n",
-			sb->s_id, statestr, function, line, error, errstr, &vaf);
+			sb->s_id, statestr, function, line, error, errstr, PV_VAL(vaf));
 		va_end(args);
 	} else {
 		pr_crit("BTRFS: error (device %s%s) in %s:%d: error=%d %s\n",
@@ -215,7 +214,7 @@ static struct ratelimit_state printk_limits[] = {
 void __cold _btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...)
 {
 	char lvl[PRINTK_MAX_SINGLE_HEADER_LEN + 1] = "\0";
-	struct va_format vaf;
+	DECLARE_PV(vaf);
 	va_list args;
 	int kern_level;
 	const char *type = logtypes[4];
@@ -239,18 +238,17 @@ void __cold _btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt,
 		fmt += size;
 	}
 
-	vaf.fmt = fmt;
+	PV_ASSIGN(vaf, fmt, args);
-	vaf.va = &args;
 
 	if (__ratelimit(ratelimit)) {
 		if (fs_info) {
 			char statestr[STATE_STRING_BUF_LEN];
 
 			btrfs_state_to_string(fs_info, statestr);
-			_printk("%sBTRFS %s (device %s%s): %pV\n", lvl, type,
+			_printk("%sBTRFS %s (device %s%s): " PV_FMT "\n", lvl, type,
-				fs_info->sb->s_id, statestr, &vaf);
+				fs_info->sb->s_id, statestr, PV_VAL(vaf));
 		} else {
-			_printk("%sBTRFS %s: %pV\n", lvl, type, &vaf);
+			_printk("%sBTRFS %s: " PV_FMT "\n", lvl, type, PV_VAL(vaf));
 		}
 	}
 
@@ -310,7 +308,7 @@ void __btrfs_panic(struct btrfs_fs_info *fs_info, const char *function,
 		   unsigned int line, int error, const char *fmt, ...)
 {
 	const char *errstr;
-	struct va_format vaf = { .fmt = fmt };
+	DECLARE_PV(vaf);
 	va_list args;
 #if 0
 	char *s_id = "<unknown>";
@@ -320,17 +318,18 @@ void __btrfs_panic(struct btrfs_fs_info *fs_info, const char *function,
 #endif
 
 	va_start(args, fmt);
-	vaf.va = &args;
+	PV_ASSIGN(vaf, fmt, args);
 
 	errstr = btrfs_decode_error(error);
 #if 0
 	if (fs_info && (btrfs_test_opt(fs_info, PANIC_ON_FATAL_ERROR)))
-		panic(KERN_CRIT "BTRFS panic (device %s) in %s:%d: %pV (error=%d %s)\n",
+		panic(KERN_CRIT "BTRFS panic (device %s) in %s:%d: " PV_FMT " (error=%d %s)\n",
-			s_id, function, line, &vaf, error, errstr);
+			s_id, function, line, PV_VAL(vaf), error, errstr);
 #endif
 
-	btrfs_crit(fs_info, "panic in %s:%d: %pV (error=%d %s)",
+
-		   function, line, &vaf, error, errstr);
+	btrfs_crit(fs_info, "panic in %s:%d: " PV_FMT " (error=%d %s)",
+		   function, line, PV_VAL(vaf), error, errstr);
 	va_end(args);
 	/* Caller calls BUG() */
 }