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 

2 files changed, 18 insertions, 11 deletions

diff --git a/include/sys/zfs_vnops.h b/include/sys/zfs_vnops.h
index f2f4d13f4..767cba10d 100644
--- a/include/sys/zfs_vnops.h
+++ b/include/sys/zfs_vnops.h
@@ -54,7 +54,7 @@ extern int zfs_mkdir(struct inode *dip, char *dirname, vattr_t *vap,
     struct inode **ipp, cred_t *cr, int flags, vsecattr_t *vsecp);
 extern int zfs_rmdir(struct inode *dip, char *name, struct inode *cwd,
     cred_t *cr, int flags);
-extern int zfs_readdir(struct inode *ip, struct dir_context *ctx, cred_t *cr);
+extern int zfs_readdir(struct inode *ip, zpl_dir_context_t *ctx, cred_t *cr);
 extern int zfs_fsync(struct inode *ip, int syncflag, cred_t *cr);
 extern int zfs_getattr(struct inode *ip, vattr_t *vap, int flag, cred_t *cr);
 extern int zfs_getattr_fast(struct inode *ip, struct kstat *sp);
diff --git a/include/sys/zpl.h b/include/sys/zpl.h
index 1f97f2511..65ed43136 100644
--- a/include/sys/zpl.h
+++ b/include/sys/zpl.h
@@ -125,56 +125,63 @@ extern const struct inode_operations zpl_ops_shares;
 
 #if defined(HAVE_VFS_ITERATE) || defined(HAVE_VFS_ITERATE_SHARED)
 
-#define	DIR_CONTEXT_INIT(_dirent, _actor, _pos) {	\
+#define	ZPL_DIR_CONTEXT_INIT(_dirent, _actor, _pos) {	\
 	.actor = _actor,				\
 	.pos = _pos,					\
 }
 
+typedef struct dir_context zpl_dir_context_t;
+
+#define	zpl_dir_emit		dir_emit
+#define	zpl_dir_emit_dot	dir_emit_dot
+#define	zpl_dir_emit_dotdot	dir_emit_dotdot
+#define	zpl_dir_emit_dots	dir_emit_dots
+
 #else
 
-typedef struct dir_context {
+typedef struct zpl_dir_context {
 	void *dirent;
 	const filldir_t actor;
 	loff_t pos;
-} dir_context_t;
+} zpl_dir_context_t;
 
-#define	DIR_CONTEXT_INIT(_dirent, _actor, _pos) {	\
+#define	ZPL_DIR_CONTEXT_INIT(_dirent, _actor, _pos) {	\
 	.dirent = _dirent,				\
 	.actor = _actor,				\
 	.pos = _pos,					\
 }
 
 static inline bool
-dir_emit(struct dir_context *ctx, const char *name, int namelen,
+zpl_dir_emit(zpl_dir_context_t *ctx, const char *name, int namelen,
     uint64_t ino, unsigned type)
 {
 	return (!ctx->actor(ctx->dirent, name, namelen, ctx->pos, ino, type));
 }
 
 static inline bool
-dir_emit_dot(struct file *file, struct dir_context *ctx)
+zpl_dir_emit_dot(struct file *file, zpl_dir_context_t *ctx)
 {
 	return (ctx->actor(ctx->dirent, ".", 1, ctx->pos,
 	    file_inode(file)->i_ino, DT_DIR) == 0);
 }
 
 static inline bool
-dir_emit_dotdot(struct file *file, struct dir_context *ctx)
+zpl_dir_emit_dotdot(struct file *file, zpl_dir_context_t *ctx)
 {
 	return (ctx->actor(ctx->dirent, "..", 2, ctx->pos,
 	    parent_ino(file_dentry(file)), DT_DIR) == 0);
 }
 
 static inline bool
-dir_emit_dots(struct file *file, struct dir_context *ctx)
+zpl_dir_emit_dots(struct file *file, zpl_dir_context_t *ctx)
 {
 	if (ctx->pos == 0) {
-		if (!dir_emit_dot(file, ctx))
+		if (!zpl_dir_emit_dot(file, ctx))
 			return (false);
 		ctx->pos = 1;
 	}
 	if (ctx->pos == 1) {
-		if (!dir_emit_dotdot(file, ctx))
+		if (!zpl_dir_emit_dotdot(file, ctx))
 			return (false);
 		ctx->pos = 2;
 	}