Linux 6.8 compat: use splice_copy_file_range() for fallback

Linux 6.8 removes generic_copy_file_range(), which had been reduced to a
simple wrapper around splice_copy_file_range(). Detect that function
directly and use it if generic_ is not available.

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes openzfs#15930 
Closes openzfs#15931

config/kernel-vfs-file_range.m4

@@ -16,6 +16,9 @@ dnl #
 dnl # 5.3: VFS copy_file_range() expected to do its own fallback,
 dnl #      generic_copy_file_range() added to support it
 dnl #
+dnl # 6.8: generic_copy_file_range() removed, replaced by
+dnl #      splice_copy_file_range()
+dnl #
 AC_DEFUN([ZFS_AC_KERNEL_SRC_VFS_COPY_FILE_RANGE], [
 	ZFS_LINUX_TEST_SRC([vfs_copy_file_range], [
 		#include <linux/fs.h>
@@ -72,6 +75,30 @@ AC_DEFUN([ZFS_AC_KERNEL_VFS_GENERIC_COPY_FILE_RANGE], [
 	])
 ])
 
+AC_DEFUN([ZFS_AC_KERNEL_SRC_VFS_SPLICE_COPY_FILE_RANGE], [
+	ZFS_LINUX_TEST_SRC([splice_copy_file_range], [
+		#include <linux/splice.h>
+	], [
+		struct file *src_file __attribute__ ((unused)) = NULL;
+		loff_t src_off __attribute__ ((unused)) = 0;
+		struct file *dst_file __attribute__ ((unused)) = NULL;
+		loff_t dst_off __attribute__ ((unused)) = 0;
+		size_t len __attribute__ ((unused)) = 0;
+		splice_copy_file_range(src_file, src_off, dst_file, dst_off,
+		    len);
+	])
+])
+AC_DEFUN([ZFS_AC_KERNEL_VFS_SPLICE_COPY_FILE_RANGE], [
+	AC_MSG_CHECKING([whether splice_copy_file_range() is available])
+	ZFS_LINUX_TEST_RESULT([splice_copy_file_range], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_VFS_SPLICE_COPY_FILE_RANGE, 1,
+		    [splice_copy_file_range() is available])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
 AC_DEFUN([ZFS_AC_KERNEL_SRC_VFS_CLONE_FILE_RANGE], [
 	ZFS_LINUX_TEST_SRC([vfs_clone_file_range], [
 		#include <linux/fs.h>

config/kernel.m4

@@ -118,6 +118,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
 	ZFS_AC_KERNEL_SRC_VFS_IOV_ITER
 	ZFS_AC_KERNEL_SRC_VFS_COPY_FILE_RANGE
 	ZFS_AC_KERNEL_SRC_VFS_GENERIC_COPY_FILE_RANGE
+	ZFS_AC_KERNEL_SRC_VFS_SPLICE_COPY_FILE_RANGE
 	ZFS_AC_KERNEL_SRC_VFS_REMAP_FILE_RANGE
 	ZFS_AC_KERNEL_SRC_VFS_CLONE_FILE_RANGE
 	ZFS_AC_KERNEL_SRC_VFS_DEDUPE_FILE_RANGE
@@ -266,6 +267,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
 	ZFS_AC_KERNEL_VFS_IOV_ITER
 	ZFS_AC_KERNEL_VFS_COPY_FILE_RANGE
 	ZFS_AC_KERNEL_VFS_GENERIC_COPY_FILE_RANGE
+	ZFS_AC_KERNEL_VFS_SPLICE_COPY_FILE_RANGE
 	ZFS_AC_KERNEL_VFS_REMAP_FILE_RANGE
 	ZFS_AC_KERNEL_VFS_CLONE_FILE_RANGE
 	ZFS_AC_KERNEL_VFS_DEDUPE_FILE_RANGE

module/os/linux/zfs/zpl_file_range.c

@@ -26,6 +26,9 @@
 #include <linux/compat.h>
 #endif
 #include <linux/fs.h>
+#ifdef HAVE_VFS_SPLICE_COPY_FILE_RANGE
+#include <linux/splice.h>
+#endif
 #include <sys/file.h>
 #include <sys/zfs_znode.h>
 #include <sys/zfs_vnops.h>
@@ -102,7 +105,7 @@ zpl_copy_file_range(struct file *src_file, loff_t src_off,
 	ret = zpl_clone_file_range_impl(src_file, src_off,
 	    dst_file, dst_off, len);
 
-#ifdef HAVE_VFS_GENERIC_COPY_FILE_RANGE
+#if defined(HAVE_VFS_GENERIC_COPY_FILE_RANGE)
 	/*
 	 * Since Linux 5.3 the filesystem driver is responsible for executing
 	 * an appropriate fallback, and a generic fallback function is provided.
@@ -111,14 +114,23 @@ zpl_copy_file_range(struct file *src_file, loff_t src_off,
 	    ret == -EAGAIN)
 		ret = generic_copy_file_range(src_file, src_off, dst_file,
 		    dst_off, len, flags);
+#elif defined(HAVE_VFS_SPLICE_COPY_FILE_RANGE)
+	/*
+	 * Since 6.8 the fallback function is called splice_copy_file_range
+	 * and has a slightly different signature.
+	 */
+	if (ret == -EOPNOTSUPP || ret == -EINVAL || ret == -EXDEV ||
+	    ret == -EAGAIN)
+		ret = splice_copy_file_range(src_file, src_off, dst_file,
+		    dst_off, len);
 #else
 	/*
 	 * Before Linux 5.3 the filesystem has to return -EOPNOTSUPP to signal
 	 * to the kernel that it should fallback to a content copy.
 	 */
 	if (ret == -EINVAL || ret == -EXDEV || ret == -EAGAIN)
 		ret = -EOPNOTSUPP;
-#endif /* HAVE_VFS_GENERIC_COPY_FILE_RANGE */
+#endif /* HAVE_VFS_GENERIC_COPY_FILE_RANGE || HAVE_VFS_SPLICE_COPY_FILE_RANGE */
 
 	return (ret);
 }