Switch to .iterate_shared

Since v4.6-rc3-29-g6192269444eb there has been a special readdir VFS
method that can be called for the same directory multiple times in
parallel, without any additional VFS locking. The VFS has provided a
WRAP_DIR_ITER() macro to re-wrap the method with extra locking, in case
the method wasn't safe for this.

With el10, the old .readdir method is now gone, and we have no choice
but to either use the wrapper, or just hook up our readdir() method to
the .iterate_shared op.

From what I can see, our implementation is safe to do this.

Signed-off-by: Auke Kok <auke.kok@versity.com>

kmod/src/Makefile.kernelcompat

@@ -609,6 +609,14 @@ ifneq (,$(shell grep 'ssize_t generic_file_splice_read.struct file' include/linu
 ccflags-y += -DKC_HAVE_GENERIC_FILE_SPLICE_READ
 endif
 
+#
+# v4.6-rc3-29-g6192269444eb
+#
+# Adds .iterate_shared readdir() iterator vfs method.
+ifneq (,$(shell grep 'iterate_shared...struct file.., struct dir_context' include/linux/fs.h))
+ccflags-y += -DKC_HAVE_ITERATE_SHARED
+endif
+
 #
 # v6.15-13744-g41cb08555c41
 #

kmod/src/dir.c

@@ -2041,7 +2041,11 @@ const struct inode_operations scoutfs_symlink_iops = {
 };
 
 const struct file_operations scoutfs_dir_fops = {
+#ifdef KC_HAVE_ITERATE_SHARED
+	.iterate_shared	= scoutfs_readdir,
+#else
 	.iterate	= scoutfs_readdir,
+#endif
 #ifdef KC_FMODE_KABI_ITERATE
 	.open		= scoutfs_dir_open,
 #endif