[PATCH for 7.1] linux-user: fix compat with glibc >= 2.36 sys/mount.h

[Daniel P . Berrangé]

The latest glibc 2.36 has extended sys/mount.h so that it
defines the FSCONFIG_* enum constants. These are historically
defined in linux/mount.h, and thus if you include both headers
the compiler complains:

In file included from /usr/include/linux/fs.h:19,
                 from ../linux-user/syscall.c:98:
/usr/include/linux/mount.h:95:6: error: redeclaration of 'enum fsconfig_command'
   95 | enum fsconfig_command {
      |      ^~~~~~~~~~~~~~~~
In file included from ../linux-user/syscall.c:31:
/usr/include/sys/mount.h:189:6: note: originally defined here
  189 | enum fsconfig_command
      |      ^~~~~~~~~~~~~~~~
/usr/include/linux/mount.h:96:9: error: redeclaration of enumerator 
'FSCONFIG_SET_FLAG'
   96 |         FSCONFIG_SET_FLAG       = 0,    /* Set parameter, supplying no 
value */
      |         ^~~~~~~~~~~~~~~~~
/usr/include/sys/mount.h:191:3: note: previous definition of 
'FSCONFIG_SET_FLAG' with type 'enum fsconfig_command'
  191 |   FSCONFIG_SET_FLAG       = 0,    /* Set parameter, supplying no value 
*/
      |   ^~~~~~~~~~~~~~~~~
...snip...

QEMU doesn't include linux/mount.h, but it does use
linux/fs.h and thus gets linux/mount.h indirectly.

glibc acknowledges this problem but does not appear to
be intending to fix it in the forseeable future, simply
documenting it as a known incompatibility with no
workaround:

  
https://sourceware.org/glibc/wiki/Release/2.36#Usage_of_.3Clinux.2Fmount.h.3E_and_.3Csys.2Fmount.h.3E
  https://sourceware.org/glibc/wiki/Synchronizing_Headers

To address this requires either removing use of sys/mount.h
or linux/fs.h, despite QEMU needing declarations from
both.

This patch removes linux/fs.h, meaning we have to define
various FS_IOC constants that are now unavailable.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 linux-user/syscall.c | 18 ++++++++++++++++++
 meson.build          |  2 ++
 2 files changed, 20 insertions(+)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index b27a6552aa..52d178afe7 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -95,7 +95,25 @@
 #include <linux/soundcard.h>
 #include <linux/kd.h>
 #include <linux/mtio.h>
+
+#ifdef HAVE_SYS_MOUNT_FSCONFIG
+/*
+ * glibc >= 2.36 linux/mount.h conflicts with sys/mount.h,
+ * which in turn prevents use of linux/fs.h. So we have to
+ * define the constants ourselves for now.
+ */
+#define FS_IOC_GETFLAGS                _IOR('f', 1, long)
+#define FS_IOC_SETFLAGS                _IOW('f', 2, long)
+#define FS_IOC_GETVERSION              _IOR('v', 1, long)
+#define FS_IOC_SETVERSION              _IOW('v', 2, long)
+#define FS_IOC_FIEMAP                  _IOWR('f', 11, struct fiemap)
+#define FS_IOC32_GETFLAGS              _IOR('f', 1, int)
+#define FS_IOC32_SETFLAGS              _IOW('f', 2, int)
+#define FS_IOC32_GETVERSION            _IOR('v', 1, int)
+#define FS_IOC32_SETVERSION            _IOW('v', 2, int)
+#else
 #include <linux/fs.h>
+#endif
 #include <linux/fd.h>
 #if defined(CONFIG_FIEMAP)
 #include <linux/fiemap.h>
diff --git a/meson.build b/meson.build
index 294e9a8f32..30a380752c 100644
--- a/meson.build
+++ b/meson.build
@@ -1963,6 +1963,8 @@ config_host_data.set('HAVE_OPTRESET',
                      cc.has_header_symbol('getopt.h', 'optreset'))
 config_host_data.set('HAVE_IPPROTO_MPTCP',
                      cc.has_header_symbol('netinet/in.h', 'IPPROTO_MPTCP'))
+config_host_data.set('HAVE_SYS_MOUNT_FSCONFIG',
+                     cc.has_header_symbol('sys/mount.h', 'FSCONFIG_SET_FLAG'))
 
 # has_member
 config_host_data.set('HAVE_SIGEV_NOTIFY_THREAD_ID',
-- 
2.37.1