Linux 4.11 compat: iops.getattr and friends

In torvalds/linux@a528d35, there are changes to the getattr family of functions,
struct kstat, and the interface of inode_operations .getattr.

The inode_operations .getattr and simple_getattr() interface changed to:

int (*getattr) (const struct path *, struct dentry *, struct kstat *,
    u32 request_mask, unsigned int query_flags)

The request_mask argument indicates which field(s) the caller intends to use.
Fields the caller has not specified via request_mask may be set in the returned
struct anyway, but their values may be approximate.

The query_flags argument indicates whether the filesystem must update
the attributes from the backing store.

Currently both fields are ignored.  It is possible that getattr-related
functions within zfs could be optimized based on the request_mask.

struct kstat includes new fields:
u32               result_mask;  /* What fields the user got */
u64               attributes;   /* See STATX_ATTR_* flags */
struct timespec   btime;        /* File creation time */

Fields attribute and btime are cleared; the result_mask reflects this.  These
appear to be optional based on simple_getattr() and vfs_getattr() within the
kernel, which take the same approach.

Reviewed-by: Chunwei Chen <david.chen@osnexus.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes openzfs#5875

config/kernel-inode-getattr.m4

@@ -0,0 +1,67 @@
+dnl #
+dnl # Linux 4.11 API
+dnl # See torvalds/linux@a528d35
+dnl #
+AC_DEFUN([ZFS_AC_PATH_KERNEL_IOPS_GETATTR], [
+	AC_MSG_CHECKING([whether iops->getattr() takes a path])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/fs.h>
+
+		int test_getattr(
+		    const struct path *p, struct kstat *k,
+		    u32 request_mask, unsigned int query_flags)
+		    { return 0; }
+
+		static const struct inode_operations
+		    iops __attribute__ ((unused)) = {
+			.getattr = test_getattr,
+		};
+	],[
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_PATH_IOPS_GETATTR, 1,
+		    [iops->getattr() takes a path])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
+
+
+dnl #
+dnl # Linux 3.9 - 4.10 API
+dnl #
+AC_DEFUN([ZFS_AC_VFSMOUNT_KERNEL_IOPS_GETATTR], [
+	AC_MSG_CHECKING([whether iops->getattr() takes a vfsmount])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/fs.h>
+
+		int test_getattr(
+		    struct vfsmount *mnt, struct dentry *d,
+		    struct kstat *k)
+		    { return 0; }
+
+		static const struct inode_operations
+		    iops __attribute__ ((unused)) = {
+			.getattr = test_getattr,
+		};
+	],[
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_VFSMOUNT_IOPS_GETATTR, 1,
+		    [iops->getattr() takes a vfsmount])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
+
+dnl #
+dnl # The interface of the getattr callback from the inode_operations
+dnl # structure changed.  Also, the interface of the simple_getattr()
+dnl # function provided by the kernel changed.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_INODE_OPERATIONS_GETATTR], [
+	ZFS_AC_PATH_KERNEL_IOPS_GETATTR
+	ZFS_AC_VFSMOUNT_KERNEL_IOPS_GETATTR
+])

config/kernel.m4

@@ -58,6 +58,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_INODE_OPERATIONS_CHECK_ACL_WITH_FLAGS
 	ZFS_AC_KERNEL_INODE_OPERATIONS_GET_ACL
 	ZFS_AC_KERNEL_INODE_OPERATIONS_SET_ACL
+	ZFS_AC_KERNEL_INODE_OPERATIONS_GETATTR
 	ZFS_AC_KERNEL_GET_ACL_HANDLE_CACHE
 	ZFS_AC_KERNEL_SHOW_OPTIONS
 	ZFS_AC_KERNEL_FILE_INODE

include/linux/vfs_compat.h

@@ -368,4 +368,47 @@ setattr_prepare(struct dentry *dentry, struct iattr *ia)
 }
 #endif
 
+/*
+ * 4.11 API change
+ * These macros are defined by kernel 4.11.  We define them so that the same
+ * code builds under kernels < 4.11 and >= 4.11.  The macros are set to 0 so
+ * that it will create obvious failures if they are accidentally used when built
+ * against a kernel >= 4.11.
+ */
+
+#ifndef STATX_BASIC_STATS
+#define	STATX_BASIC_STATS	0
+#endif
+
+#ifndef AT_STATX_SYNC_AS_STAT
+#define	AT_STATX_SYNC_AS_STAT	0
+#endif
+
+/*
+ * 4.11 API change
+ * 4.11 takes struct path *, < 4.11 takes vfsmount *
+ */
+
+#ifdef HAVE_VFSMOUNT_IOPS_GETATTR
+#define	ZPL_GETATTR_WRAPPER(func)					\
+static int								\
+func(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)	\
+{									\
+	struct path path = { .mnt = mnt, .dentry = dentry };		\
+	return func##_impl(&path, stat, STATX_BASIC_STATS,		\
+	    AT_STATX_SYNC_AS_STAT);					\
+}
+#elif defined(HAVE_PATH_IOPS_GETATTR)
+#define	ZPL_GETATTR_WRAPPER(func)					\
+static int								\
+func(const struct path *path, struct kstat *stat, u32 request_mask,	\
+    unsigned int query_flags)						\
+{									\
+	return (func##_impl(path, stat, request_mask, query_flags));	\
+}
+#else
+#error
+#endif
+
+
 #endif /* _ZFS_VFS_H */

module/zfs/zpl_ctldir.c

@@ -100,16 +100,15 @@ zpl_root_readdir(struct file *filp, void *dirent, filldir_t filldir)
  */
 /* ARGSUSED */
 static int
-zpl_root_getattr(struct vfsmount *mnt, struct dentry *dentry,
-    struct kstat *stat)
+zpl_root_getattr_impl(const struct path *path, struct kstat *stat,
+    u32 request_mask, unsigned int query_flags)
 {
-	int error;
-
-	error = simple_getattr(mnt, dentry, stat);
+	generic_fillattr(path->dentry->d_inode, stat);
 	stat->atime = CURRENT_TIME;
 
-	return (error);
+	return (0);
 }
+ZPL_GETATTR_WRAPPER(zpl_root_getattr);
 
 static struct dentry *
 #ifdef HAVE_LOOKUP_NAMEIDATA
@@ -375,21 +374,21 @@ zpl_snapdir_mkdir(struct inode *dip, struct dentry *dentry, zpl_umode_t mode)
  */
 /* ARGSUSED */
 static int
-zpl_snapdir_getattr(struct vfsmount *mnt, struct dentry *dentry,
-    struct kstat *stat)
+zpl_snapdir_getattr_impl(const struct path *path, struct kstat *stat,
+    u32 request_mask, unsigned int query_flags)
 {
-	zfs_sb_t *zsb = ITOZSB(dentry->d_inode);
-	int error;
+	zfs_sb_t *zsb = ITOZSB(path->dentry->d_inode);
 
 	ZFS_ENTER(zsb);
-	error = simple_getattr(mnt, dentry, stat);
+	generic_fillattr(path->dentry->d_inode, stat);
 	stat->nlink = stat->size = 2;
 	stat->ctime = stat->mtime = dmu_objset_snap_cmtime(zsb->z_os);
 	stat->atime = CURRENT_TIME;
 	ZFS_EXIT(zsb);
 
-	return (error);
+	return (0);
 }
+ZPL_GETATTR_WRAPPER(zpl_snapdir_getattr);
 
 /*
  * The '.zfs/snapshot' directory file operations.  These mainly control
@@ -509,22 +508,22 @@ zpl_shares_readdir(struct file *filp, void *dirent, filldir_t filldir)
 
 /* ARGSUSED */
 static int
-zpl_shares_getattr(struct vfsmount *mnt, struct dentry *dentry,
-    struct kstat *stat)
+zpl_shares_getattr_impl(const struct path *path, struct kstat *stat,
+    u32 request_mask, unsigned int query_flags)
 {
-	struct inode *ip = dentry->d_inode;
+	struct inode *ip = path->dentry->d_inode;
 	zfs_sb_t *zsb = ITOZSB(ip);
 	znode_t *dzp;
 	int error;
 
 	ZFS_ENTER(zsb);
 
 	if (zsb->z_shares_dir == 0) {
-		error = simple_getattr(mnt, dentry, stat);
+		generic_fillattr(path->dentry->d_inode, stat);
 		stat->nlink = stat->size = 2;
 		stat->atime = CURRENT_TIME;
 		ZFS_EXIT(zsb);
-		return (error);
+		return (0);
 	}
 
 	error = -zfs_zget(zsb, zsb->z_shares_dir, &dzp);
@@ -538,6 +537,7 @@ zpl_shares_getattr(struct vfsmount *mnt, struct dentry *dentry,
 
 	return (error);
 }
+ZPL_GETATTR_WRAPPER(zpl_shares_getattr);
 
 /*
  * The '.zfs/shares' directory file operations.

module/zfs/zpl_inode.c

@@ -302,18 +302,25 @@ zpl_rmdir(struct inode * dir, struct dentry *dentry)
 }
 
 static int
-zpl_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
+zpl_getattr_impl(const struct path *path, struct kstat *stat, u32 request_mask,
+    unsigned int query_flags)
 {
 	int error;
 	fstrans_cookie_t cookie;
 
 	cookie = spl_fstrans_mark();
-	error = -zfs_getattr_fast(dentry->d_inode, stat);
+
+	/*
+	 * XXX request_mask and query_flags currently ignored.
+	 */
+
+	error = -zfs_getattr_fast(path->dentry->d_inode, stat);
 	spl_fstrans_unmark(cookie);
 	ASSERT3S(error, <=, 0);
 
 	return (error);
 }
+ZPL_GETATTR_WRAPPER(zpl_getattr);
 
 static int
 zpl_setattr(struct dentry *dentry, struct iattr *ia)