Linux 6.12: f_version removed from struct file

linux/torvalds@11068e0b64cb removes it, suggesting this was a always
there as a helper to handle concurrent seeks, which all filesystems now
handle themselves if necessary.

Without looking into the mechanism, I can imagine how it might have been
used, but we have always set it to zero and never read from it,
presumably because we've always tracked per-caller position through the
znode anyway. So I don't see how there can be any functional change for
us by removing it. I've stayed conservative though and left it in for
older kernels, since its clearly not hurting anything there.

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes openzfs#16582

config/kernel-file.m4

@@ -0,0 +1,31 @@
+dnl #
+dnl # 6.12 removed f_version from struct file
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_FILE_F_VERSION], [
+	ZFS_LINUX_TEST_SRC([file_f_version], [
+		#include <linux/fs.h>
+
+		static const struct f __attribute__((unused)) = {
+			.f_version = 0;
+		};
+	])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_FILE_F_VERSION], [
+	AC_MSG_CHECKING([whether file->f_version exists])
+	ZFS_LINUX_TEST_RESULT([file_f_version], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_FILE_F_VERSION, 1,
+		    [file->f_version exists])
+	], [
+		AC_MSG_RESULT(no)
+	])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_FILE], [
+	ZFS_AC_KERNEL_FILE_F_VERSION
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_SRC_FILE], [
+	ZFS_AC_KERNEL_SRC_FILE_F_VERSION
+])

config/kernel.m4

@@ -172,6 +172,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
 	ZFS_AC_KERNEL_SRC_SYNC_BDEV
 	ZFS_AC_KERNEL_SRC_MM_PAGE_SIZE
 	ZFS_AC_KERNEL_SRC_MM_PAGE_MAPPING
+	ZFS_AC_KERNEL_SRC_FILE
 	case "$host_cpu" in
 		powerpc*)
 			ZFS_AC_KERNEL_SRC_CPU_HAS_FEATURE
@@ -327,6 +328,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
 	ZFS_AC_KERNEL_MM_PAGE_SIZE
 	ZFS_AC_KERNEL_MM_PAGE_MAPPING
 	ZFS_AC_KERNEL_1ARG_ASSIGN_STR
+	ZFS_AC_KERNEL_FILE
 	case "$host_cpu" in
 		powerpc*)
 			ZFS_AC_KERNEL_CPU_HAS_FEATURE

include/os/linux/kernel/linux/vfs_compat.h

@@ -167,7 +167,9 @@ lseek_execute(
 	if (offset != filp->f_pos) {
 		spin_lock(&filp->f_lock);
 		filp->f_pos = offset;
+#ifdef HAVE_FILE_F_VERSION
 		filp->f_version = 0;
+#endif
 		spin_unlock(&filp->f_lock);
 	}