RHEL 7.5 compat: FMODE_KABI_ITERATE

As of RHEL 7.5 the mainline fops.iterate() method was added to
the file_operations structure and is correctly detected by the
configure script.

Normally this is what we want, but in order to maintain KABI
compatibility the RHEL change additionally does the following:

* Requires that callers intending to use this extended interface
  set the FMODE_KABI_ITERATE flag on the file structure when
  opening the directory.
* Adds the fops.iterate() method to the end of the structure,
  without removing fops.readdir().

This change updates the configure check to ignore the RHEL 7.5+
variant of fops.iterate() when detected.  Instead fallback to
the fops.readdir() interface which will be available.

Finally, add the 'zpl_' prefix to the directory context wrappers
to avoid colliding with the kernel provided symbols when both
the fops.iterate() and fops.readdir() are provided by the kernel.

Reviewed-by: Olaf Faaland <[email protected]>
Reviewed-by: Tony Hutter <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #7460 
Closes #7463 

1 files changed, 16 insertions, 5 deletions

diff --git a/config/kernel-vfs-iterate.m4 b/config/kernel-vfs-iterate.m4
index 7b1599e13..5de901d44 100644
--- a/config/kernel-vfs-iterate.m4
+++ b/config/kernel-vfs-iterate.m4
@@ -23,16 +23,27 @@ AC_DEFUN([ZFS_AC_KERNEL_VFS_ITERATE], [
 		dnl #
 		dnl # 3.11 API change
 		dnl #
+		dnl # RHEL 7.5 compatibility; the fops.iterate() method was
+		dnl # added to the file_operations structure but in order to
+		dnl # maintain KABI compatibility all callers must set
+		dnl # FMODE_KABI_ITERATE which is checked in iterate_dir().
+		dnl # When detected ignore this interface and fallback to
+		dnl # to using fops.readdir() to retain KABI compatibility.
+		dnl #
 		AC_MSG_CHECKING([whether fops->iterate() is available])
 		ZFS_LINUX_TRY_COMPILE([
 			#include <linux/fs.h>
-			int iterate(struct file *filp, struct dir_context * context)
-			    { return 0; }
+			int iterate(struct file *filp,
+			    struct dir_context *context) { return 0; }
 
 			static const struct file_operations fops
 			    __attribute__ ((unused)) = {
 				.iterate	 = iterate,
 			};
+
+			#if defined(FMODE_KABI_ITERATE)
+			#error "RHEL 7.5, FMODE_KABI_ITERATE interface"
+			#endif
 		],[
 		],[
 			AC_MSG_RESULT(yes)
@@ -44,8 +55,8 @@ AC_DEFUN([ZFS_AC_KERNEL_VFS_ITERATE], [
 			AC_MSG_CHECKING([whether fops->readdir() is available])
 			ZFS_LINUX_TRY_COMPILE([
 				#include <linux/fs.h>
-				int readdir(struct file *filp, void *entry, filldir_t func)
-				    { return 0; }
+				int readdir(struct file *filp, void *entry,
+				    filldir_t func) { return 0; }
 
 				static const struct file_operations fops
 				    __attribute__ ((unused)) = {
@@ -57,7 +68,7 @@ AC_DEFUN([ZFS_AC_KERNEL_VFS_ITERATE], [
 				AC_DEFINE(HAVE_VFS_READDIR, 1,
 					  [fops->readdir() is available])
 			],[
-				AC_MSG_ERROR(no; file a bug report with ZFSOnLinux)
+				AC_MSG_ERROR(no; file a bug report with ZoL)
 			])
 		])
 	])