package/btrfs-progs/0002-btrfs-progs-add-uClibc-ng-compatibility-for-printf-f.patch

From 0f34a362c8644f212138fb8de8e0fba54941e757 Mon Sep 17 00:00:00 2001
From: Julien Olivain <ju.o@free.fr>
Date: Sun, 14 Jul 2024 16:28:08 +0200
Subject: [PATCH] btrfs-progs: add uClibc-ng compatibility for printf format
 %pV

Commit [1] 164bc10d "btrfs-progs: add musl compatibility for printf
format %pV" added a logic to detect the presence of the glibc
<printf.h> header, and if present, to use the
register_printf_specifier() and register_printf_modifier() functions.

The original intent (as the commit log suggests), was to support the
musl libc, which does not provides this <printf.h> header.

When compiling with another libc, such as uClibc-ng, btrfs-progs fail
to build with error:

    common/messages.c: In function 'print_va_format':
    common/messages.c:51:19: error: 'const struct printf_info' has no member named 'user'
       51 |         if (!(info->user & va_modifier))
          |                   ^~
    common/messages.c: In function 'btrfs_no_printk':
    common/messages.c:76:17: warning: implicit declaration of function 'register_printf_specifier'; did you mean 'register_printf_function'? [-Wimplicit-function-declaration]
       76 |                 register_printf_specifier('V', print_va_format,
          |                 ^~~~~~~~~~~~~~~~~~~~~~~~~
          |                 register_printf_function
    common/messages.c:78:31: warning: implicit declaration of function 'register_printf_modifier'; did you mean 'register_printf_function'? [-Wimplicit-function-declaration]
       78 |                 va_modifier = register_printf_modifier(L"p");
          |                               ^~~~~~~~~~~~~~~~~~~~~~~~
          |                               register_printf_function

This is because uClibc-ng provides a <printf.h> header, but not the
register_printf_specifier() and register_printf_modifier() functions.
See [2]. It mainly includes register_printf_function(). uClibc-ng
emulates an older glibc behavior. Glibc added support for printf user
elements in commit [3] (first included in glibc-2.10, in 2009). Checking
only the <printf.h> is not sufficient.

This commit fixes this build issue by refining the detection logic of
the <printf.h> functions required by btrfs-progs.

[1] https://github.com/kdave/btrfs-progs/commit/164bc10dfc08d8754d23ef0d6d7281e139d6cd53
[2] https://gogs.waldemar-brodkorb.de/oss/uclibc-ng/src/v1.0.49/include/printf.h
[3] https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=9d26efa90c6dcbcd6b3e586c9927b6058ef4d529

Upstream: Proposed: https://github.com/kdave/btrfs-progs/pull/843
Signed-off-by: Julien Olivain <ju.o@free.fr>
---
 common/messages.h | 4 +++-
 configure.ac      | 4 ++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/common/messages.h b/common/messages.h
index d6d4044d..aced7c9b 100644
--- a/common/messages.h
+++ b/common/messages.h
@@ -25,7 +25,9 @@
 /*
  * Workaround for custom format %pV that may not be supported on all libcs.
  */
-#ifdef HAVE_PRINTF_H
+#if defined(HAVE_PRINTF_H) \
+	&& defined(HAVE_REGISTER_PRINTF_SPECIFIER) \
+	&& defined(HAVE_REGISTER_PRINTF_MODIFIER)
 #define DECLARE_PV(name)		struct va_format name
 #define PV_FMT				"%pV"
 #define PV_VAL(va)			&va
diff --git a/configure.ac b/configure.ac
index b69973b3..62b88973 100644
--- a/configure.ac
+++ b/configure.ac
@@ -95,6 +95,10 @@ AC_CHECK_HEADERS([linux/hw_breakpoint.h])
 AC_CHECK_HEADERS([linux/fsverity.h])
 AC_CHECK_HEADERS([printf.h])
 
+dnl Check for printf.h functions.
+AC_CHECK_FUNCS([register_printf_specifier])
+AC_CHECK_FUNCS([register_printf_modifier])
+
 if grep -q 'HAVE_LINUX_FSVERITY_H.*1' confdefs.h; then
 	have_fsverity='yes'
 else
-- 
2.45.2