[PATCH 31/32] vfs: syscall: Add fsinfo() to query filesystem information [ver #9]

@@ -403,3 +403,4 @@
 389	i386	fsopen			sys_fsopen			__ia32_sys_fsopen
 390	i386	fsmount			sys_fsmount			__ia32_sys_fsmount
 391	i386	fspick			sys_fspick			__ia32_sys_fspick
+392	i386	fsinfo			sys_fsinfo			__ia32_sys_fsinfo

@@ -348,6 +348,7 @@
 337	common	fsopen			__x64_sys_fsopen
 338	common	fsmount			__x64_sys_fsmount
 339	common	fspick			__x64_sys_fspick
+340	common	fsinfo			__x64_sys_fsinfo
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact

@@ -9,6 +9,7 @@
 #include <linux/security.h>
 #include <linux/uaccess.h>
 #include <linux/compat.h>
+#include <linux/fsinfo.h>
 #include "internal.h"
 
 static int flags_by_mnt(int mnt_flags)

@@ -384,3 +385,472 @@ COMPAT_SYSCALL_DEFINE2(ustat, unsigned, dev, struct compat_ustat __user *, u)
 	return 0;
 }
 #endif
+
+/*
+ * Get basic filesystem stats from statfs.
+ */
+static int fsinfo_generic_statfs(struct dentry *dentry,
+				 struct fsinfo_statfs *p)
+{
+	struct super_block *sb;
+	struct kstatfs buf;
+	int ret;
+
+	ret = statfs_by_dentry(dentry, &buf);
+	if (ret < 0)
+		return ret;
+
+	sb = dentry->d_sb;
+	p->f_blocks	= buf.f_blocks;
+	p->f_bfree	= buf.f_bfree;
+	p->f_bavail	= buf.f_bavail;
+	p->f_files	= buf.f_files;
+	p->f_ffree	= buf.f_ffree;
+	p->f_favail	= buf.f_ffree;
+	p->f_bsize	= buf.f_bsize;
+	p->f_frsize	= buf.f_frsize;
+	return sizeof(*p);
+}
+
+static int fsinfo_generic_ids(struct dentry *dentry,
+			      struct fsinfo_ids *p)
+{
+	struct super_block *sb;
+	struct kstatfs buf;
+	int ret;
+
+	ret = statfs_by_dentry(dentry, &buf);
+	if (ret < 0)
+		return ret;
+
+	sb = dentry->d_sb;
+	p->f_fstype	= sb->s_magic;
+	p->f_dev_major	= MAJOR(sb->s_dev);
+	p->f_dev_minor	= MINOR(sb->s_dev);
+	p->f_flags	= ST_VALID | flags_by_sb(sb->s_flags);
+
+	memcpy(&p->f_fsid, &buf.f_fsid, sizeof(p->f_fsid));
+	strcpy(p->f_fs_name, dentry->d_sb->s_type->name);
+	return sizeof(*p);
+}
+
+static int fsinfo_generic_limits(struct dentry *dentry,
+				 struct fsinfo_limits *lim)
+{
+	struct super_block *sb = dentry->d_sb;
+
+	lim->max_file_size = sb->s_maxbytes;
+	lim->max_hard_links = sb->s_max_links;
+	lim->max_uid = UINT_MAX;
+	lim->max_gid = UINT_MAX;
+	lim->max_projid = UINT_MAX;
+	lim->max_filename_len = NAME_MAX;
+	lim->max_symlink_len = PAGE_SIZE;
+	lim->max_xattr_name_len = XATTR_NAME_MAX;
+	lim->max_xattr_body_len = XATTR_SIZE_MAX;
+	lim->max_dev_major = 0xffffff;
+	lim->max_dev_minor = 0xff;
+	return sizeof(*lim);
+}
+
+static int fsinfo_generic_supports(struct dentry *dentry,
+				   struct fsinfo_supports *c)
+{
+	struct super_block *sb = dentry->d_sb;
+
+	c->stx_mask = STATX_BASIC_STATS;
+	if (sb->s_d_op && sb->s_d_op->d_automount)
+		c->stx_attributes |= STATX_ATTR_AUTOMOUNT;
+	return sizeof(*c);
+}
+
+static int fsinfo_generic_capabilities(struct dentry *dentry,
+				       struct fsinfo_capabilities *c)
+{
+	struct super_block *sb = dentry->d_sb;
+
+	if (sb->s_mtd)
+		fsinfo_set_cap(c, fsinfo_cap_is_flash_fs);
+	else if (sb->s_bdev)
+		fsinfo_set_cap(c, fsinfo_cap_is_block_fs);
+
+	if (sb->s_quota_types & QTYPE_MASK_USR)
+		fsinfo_set_cap(c, fsinfo_cap_user_quotas);
+	if (sb->s_quota_types & QTYPE_MASK_GRP)
+		fsinfo_set_cap(c, fsinfo_cap_group_quotas);
+	if (sb->s_quota_types & QTYPE_MASK_PRJ)
+		fsinfo_set_cap(c, fsinfo_cap_project_quotas);
+	if (sb->s_d_op && sb->s_d_op->d_automount)
+		fsinfo_set_cap(c, fsinfo_cap_automounts);
+	if (sb->s_id[0])
+		fsinfo_set_cap(c, fsinfo_cap_volume_id);
+
+	fsinfo_set_cap(c, fsinfo_cap_has_atime);
+	fsinfo_set_cap(c, fsinfo_cap_has_ctime);
+	fsinfo_set_cap(c, fsinfo_cap_has_mtime);
+	return sizeof(*c);
+}
+
+static int fsinfo_generic_timestamp_info(struct dentry *dentry,
+					 struct fsinfo_timestamp_info *ts)
+{
+	struct super_block *sb = dentry->d_sb;
+
+	/* If unset, assume 1s granularity */
+	u16 mantissa = 1;
+	s8 exponent = 0;
+
+	ts->minimum_timestamp = S64_MIN;
+	ts->maximum_timestamp = S64_MAX;
+	if (sb->s_time_gran < 1000000000) {
+		if (sb->s_time_gran < 1000)
+			exponent = -9;
+		else if (sb->s_time_gran < 1000000)
+			exponent = -6;
+		else
+			exponent = -3;
+	}
+#define set_gran(x)				\
+	do {					\
+		ts->x##_mantissa = mantissa;	\
+		ts->x##_exponent = exponent;	\
+	} while (0)
+	set_gran(atime_gran);
+	set_gran(btime_gran);
+	set_gran(ctime_gran);
+	set_gran(mtime_gran);
+	return sizeof(*ts);
+}
+
+static int fsinfo_generic_volume_uuid(struct dentry *dentry,
+				      struct fsinfo_volume_uuid *vu)
+{
+	struct super_block *sb = dentry->d_sb;
+
+	memcpy(vu, &sb->s_uuid, sizeof(*vu));
+	return sizeof(*vu);
+}
+
+static int fsinfo_generic_volume_id(struct dentry *dentry, char *buf)
+{
+	struct super_block *sb = dentry->d_sb;
+	size_t len = strlen(sb->s_id);
+
+	if (buf)
+		memcpy(buf, sb->s_id, len + 1);
+	return len;
+}
+
+static int fsinfo_generic_name_encoding(struct dentry *dentry, char *buf)
+{
+	static const char encoding[] = "utf8";
+
+	if (buf)
+		memcpy(buf, encoding, sizeof(encoding) - 1);
+	return sizeof(encoding) - 1;
+}
+
+static int fsinfo_generic_io_size(struct dentry *dentry,
+				  struct fsinfo_io_size *c)
+{
+	struct super_block *sb = dentry->d_sb;
+	struct kstatfs buf;
+	int ret;
+
+	if (sb->s_op->statfs == simple_statfs) {
+		c->block_size = PAGE_SIZE;
+		c->max_single_read_size = 0;
+		c->max_single_write_size = 0;
+		c->best_read_size = PAGE_SIZE;
+		c->best_write_size = PAGE_SIZE;
+	} else {
+		ret = statfs_by_dentry(dentry, &buf);
+		if (ret < 0)
+			return ret;
+		c->block_size = buf.f_bsize;
+		c->max_single_read_size = buf.f_bsize;
+		c->max_single_write_size = buf.f_bsize;
+		c->best_read_size = PAGE_SIZE;
+		c->best_write_size = PAGE_SIZE;
+	}
+	return sizeof(*c);
+}
+
+/*
+ * Implement some queries generically from stuff in the superblock.
+ */
+int generic_fsinfo(struct dentry *dentry, struct fsinfo_kparams *params)
+{
+#define _gen(X) fsinfo_attr_##X: return fsinfo_generic_##X(dentry, params->buffer)
+
+	switch (params->request) {
+	case _gen(statfs);
+	case _gen(ids);
+	case _gen(limits);
+	case _gen(supports);
+	case _gen(capabilities);
+	case _gen(timestamp_info);
+	case _gen(volume_uuid);
+	case _gen(volume_id);
+	case _gen(name_encoding);
+	case _gen(io_size);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+EXPORT_SYMBOL(generic_fsinfo);
+
+/*
+ * Retrieve the filesystem info.  We make some stuff up if the operation is not
+ * supported.
+ */
+int vfs_fsinfo(const struct path *path, struct fsinfo_kparams *params)
+{
+	struct dentry *dentry = path->dentry;
+	int (*get_fsinfo)(struct dentry *, struct fsinfo_kparams *);
+	int ret;
+
+	if (params->request == fsinfo_attr_fsinfo) {
+		struct fsinfo_fsinfo *info = params->buffer;
+
+		info->max_attr	= fsinfo_attr__nr;
+		info->max_cap	= fsinfo_cap__nr;
+		return sizeof(*info);
+	}
+
+	get_fsinfo = dentry->d_sb->s_op->get_fsinfo;
+	if (!get_fsinfo) {
+		if (!dentry->d_sb->s_op->statfs)
+			return -EOPNOTSUPP;
+		get_fsinfo = generic_fsinfo;
+	}
+
+	ret = security_sb_statfs(dentry);
+	if (ret)
+		return ret;
+
+	ret = get_fsinfo(dentry, params);
+	if (ret < 0)
+		return ret;
+
+	if (params->request == fsinfo_attr_ids &&
+	    params->buffer) {
+		struct fsinfo_ids *p = params->buffer;
+
+		p->f_flags |= flags_by_mnt(path->mnt->mnt_flags);
+	}
+	return ret;
+}
+
+static int vfs_fsinfo_path(int dfd, const char __user *filename,
+			   struct fsinfo_kparams *params)
+{
+	struct path path;
+	unsigned lookup_flags = LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
+	int ret = -EINVAL;
+
+	if ((params->at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT |
+				 AT_EMPTY_PATH)) != 0)
+		return -EINVAL;
+
+	if (params->at_flags & AT_SYMLINK_NOFOLLOW)
+		lookup_flags &= ~LOOKUP_FOLLOW;
+	if (params->at_flags & AT_NO_AUTOMOUNT)
+		lookup_flags &= ~LOOKUP_AUTOMOUNT;
+	if (params->at_flags & AT_EMPTY_PATH)
+		lookup_flags |= LOOKUP_EMPTY;
+
+retry:
+	ret = user_path_at(dfd, filename, lookup_flags, &path);
+	if (ret)
+		goto out;
+
+	ret = vfs_fsinfo(&path, params);
+	path_put(&path);
+	if (retry_estale(ret, lookup_flags)) {
+		lookup_flags |= LOOKUP_REVAL;
+		goto retry;
+	}
+out:
+	return ret;
+}
+
+static int vfs_fsinfo_fd(unsigned int fd, struct fsinfo_kparams *params)
+{
+	struct fd f = fdget_raw(fd);
+	int ret = -EBADF;
+
+	if (f.file) {
+		ret = vfs_fsinfo(&f.file->f_path, params);
+		fdput(f);
+	}
+	return ret;
+}
+
+/*
+ * Return buffer information by requestable attribute.
+ *
+ * STRUCT indicates a fixed-size structure with only one instance.
+ * STRUCT_N indicates a fixed-size structure that may have multiple instances.
+ * STRING indicates a string with only one instance.
+ * STRING_N indicates a string that may have multiple instances.
+ * STRUCT_ARRAY indicates an array of fixed-size structs with only one instance.
+ * STRUCT_ARRAY_N as above that may have multiple instances.
+ *
+ * If an entry is marked STRUCT, STRUCT_N or STRUCT_NM then if no buffer is
+ * supplied to sys_fsinfo(), sys_fsinfo() will handle returning the buffer size
+ * without calling vfs_fsinfo() and the filesystem.
+ *
+ * No struct may have more than 252 bytes (ie. 0x3f * 4)
+ */
+#define FSINFO_STRING(N)	 [fsinfo_attr_##N] = 0x0000
+#define FSINFO_STRUCT(N)	 [fsinfo_attr_##N] = sizeof(struct fsinfo_##N)
+#define FSINFO_STRING_N(N)	 [fsinfo_attr_##N] = 0x4000
+#define FSINFO_STRUCT_N(N)	 [fsinfo_attr_##N] = 0x4000 | sizeof(struct fsinfo_##N)
+#define FSINFO_STRUCT_NM(N)	 [fsinfo_attr_##N] = 0x8000 | sizeof(struct fsinfo_##N)
+static const u16 fsinfo_buffer_sizes[fsinfo_attr__nr] = {
+	FSINFO_STRUCT		(statfs),
+	FSINFO_STRUCT		(fsinfo),
+	FSINFO_STRUCT		(ids),
+	FSINFO_STRUCT		(limits),
+	FSINFO_STRUCT		(capabilities),
+	FSINFO_STRUCT		(supports),
+	FSINFO_STRUCT		(timestamp_info),
+	FSINFO_STRING		(volume_id),
+	FSINFO_STRUCT		(volume_uuid),
+	FSINFO_STRING		(volume_name),
+	FSINFO_STRING		(cell_name),
+	FSINFO_STRING		(domain_name),
+	FSINFO_STRING		(realm_name),
+	FSINFO_STRING_N		(server_name),
+	FSINFO_STRUCT_NM	(server_address),
+	FSINFO_STRING_N		(parameter),
+	FSINFO_STRING_N		(source),
+	FSINFO_STRING		(name_encoding),
+	FSINFO_STRING		(name_codepage),
+	FSINFO_STRUCT		(io_size),
+};
+
+/**
+ * sys_fsinfo - System call to get filesystem information
+ * @dfd: Base directory to pathwalk from or fd referring to filesystem.
+ * @filename: Filesystem to query or NULL.
+ * @_params: Parameters to define request (or NULL for enhanced statfs).
+ * @_buffer: Result buffer.
+ * @buf_size: Size of result buffer.
+ *
+ * Get information on a filesystem.  The filesystem attribute to be queried is
+ * indicated by @_params->request, and some of the attributes can have multiple
+ * values, indexed by @_params->Nth and @_params->Mth.  If @_params is NULL,
+ * then the 0th fsinfo_attr_statfs attribute is queried.  If an attribute does
+ * not exist, EOPNOTSUPP is returned; if the Nth,Mth value does not exist,
+ * ENODATA is returned.
+ *
+ * On success, the size of the attribute's value is returned.  If @buf_size is
+ * 0 or @_buffer is NULL, only the size is returned.  If the size of the value
+ * is larger than @buf_size, it will be truncated by the copy.  If the size of
+ * the value is smaller than @buf_size then the excess buffer space will be
+ * cleared.  The full size of the value will be returned, irrespective of how
+ * much data is actually placed in the buffer.
+ */
+SYSCALL_DEFINE5(fsinfo,
+		int, dfd, const char __user *, filename,
+		struct fsinfo_params __user *, _params,
+		void __user *, _buffer, size_t, buf_size)
+{
+	struct fsinfo_params user_params;
+	struct fsinfo_kparams params;
+	size_t size;
+	int ret;
+
+	if (_params) {
+		if (copy_from_user(&user_params, _params, sizeof(user_params)))
+			return -EFAULT;
+		if (user_params.__reserved[0] ||
+		    user_params.__reserved[1] ||
+		    user_params.__reserved[2] ||
+		    user_params.__reserved[3] ||
+		    user_params.__reserved[4] ||
+		    user_params.__reserved[5])
+			return -EINVAL;
+		if (user_params.request >= fsinfo_attr__nr)
+			return -EOPNOTSUPP;
+		params.at_flags = user_params.at_flags;
+		params.request = user_params.request;
+		params.Nth = user_params.Nth;
+		params.Mth = user_params.Mth;
+	} else {
+		params.at_flags = 0;
+		params.request = fsinfo_attr_statfs;
+		params.Nth = 0;
+		params.Mth = 0;
+	}
+
+	if (!_buffer || !buf_size) {
+		buf_size = 0;
+		_buffer = NULL;
+	}
+
+	/* Allocate an appropriately-sized buffer.  We will truncate the
+	 * contents when we write the contents back to userspace.
+	 */
+	size = fsinfo_buffer_sizes[params.request];
+	switch (size & 0xc000) {
+	case 0x0000:
+		if (params.Nth != 0)
+			return -ENODATA;
+		/* Fall through */
+	case 0x4000:
+		if (params.Mth != 0)
+			return -ENODATA;
+		/* Fall through */
+	case 0x8000:
+		break;
+	case 0xc000:
+		return -ENOBUFS;
+	}
+
+	size &= ~0xc000;
+	if (size == 0) {
+		size = 4096; /* String */
+	} else {
+		if (buf_size == 0)
+			return size; /* We know how big the buffer should be */
+
+		/* Clear any part of the buffer that we won't fill. */
+		if (buf_size > size &&
+		    clear_user(_buffer, buf_size) != 0)
+			return -EFAULT;
+	}
+
+	if (buf_size > 0) {
+		params.buf_size = size;
+		params.buffer = kzalloc(size, GFP_KERNEL);
+		if (!params.buffer)
+			return -ENOMEM;
+	} else {
+		params.buf_size = 0;
+		params.buffer = NULL;
+	}
+
+	if (filename)
+		ret = vfs_fsinfo_path(dfd, filename, &params);
+	else
+		ret = vfs_fsinfo_fd(dfd, &params);
+	if (ret < 0)
+		goto error;
+
+	if (ret == 0) {
+		ret = -ENODATA;
+		goto error;
+	}
+
+	if (buf_size > ret)
+		buf_size = ret;
+
+	if (copy_to_user(_buffer, params.buffer, buf_size))
+		ret = -EFAULT;
+error:
+	kfree(params.buffer);
+	return ret;
+}

@@ -62,6 +62,8 @@ struct iov_iter;
 struct fscrypt_info;
 struct fscrypt_operations;
 struct fs_context;
+struct fsinfo_kparams;
+enum fsinfo_attribute;
 
 extern void __init inode_init(void);
 extern void __init inode_init_early(void);

@@ -1847,6 +1849,7 @@ struct super_operations {
 	int (*thaw_super) (struct super_block *);
 	int (*unfreeze_fs) (struct super_block *);
 	int (*statfs) (struct dentry *, struct kstatfs *);
+	int (*get_fsinfo) (struct dentry *, struct fsinfo_kparams *);
 	int (*remount_fs) (struct super_block *, int *, char *, size_t);
 	int (*reconfigure) (struct super_block *, struct fs_context *);
 	void (*umount_begin) (struct super_block *);

@@ -2223,6 +2226,7 @@ extern int iterate_mounts(int (*)(struct vfsmount *, void *), void *,
 extern int vfs_statfs(const struct path *, struct kstatfs *);
 extern int user_statfs(const char __user *, struct kstatfs *);
 extern int fd_statfs(int, struct kstatfs *);
+extern int vfs_fsinfo(const struct path *, struct fsinfo_kparams *);
 extern int freeze_super(struct super_block *super);
 extern int thaw_super(struct super_block *super);
 extern bool our_mnt(struct vfsmount *mnt);

@@ -0,0 +1,40 @@
+/* Filesystem information query
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#ifndef _LINUX_FSINFO_H
+#define _LINUX_FSINFO_H
+
+#include <uapi/linux/fsinfo.h>
+
+struct fsinfo_kparams {
+	__u32			at_flags;	/* AT_SYMLINK_NOFOLLOW and similar */
+	enum fsinfo_attribute	request;	/* What is being asking for */
+	__u32			Nth;		/* Instance of it (some may have multiple) */
+	__u32			Mth;		/* Subinstance */
+	void			*buffer;	/* Where to place the reply */
+	size_t			buf_size;	/* Size of the buffer */
+};
+
+extern int generic_fsinfo(struct dentry *, struct fsinfo_kparams *);
+
+static inline void fsinfo_set_cap(struct fsinfo_capabilities *c,
+				  enum fsinfo_capability cap)
+{
+	c->capabilities[cap / 8] |= 1 << (cap % 8);
+}
+
+static inline void fsinfo_clear_cap(struct fsinfo_capabilities *c,
+				    enum fsinfo_capability cap)
+{
+	c->capabilities[cap / 8] &= ~(1 << (cap % 8));
+}
+
+#endif /* _LINUX_FSINFO_H */

@@ -49,6 +49,7 @@ struct stat64;
 struct statfs;
 struct statfs64;
 struct statx;
+struct fsinfo_params;
 struct __sysctl_args;
 struct sysinfo;
 struct timespec;

@@ -907,6 +908,9 @@ asmlinkage long sys_move_mount(int from_dfd, const char __user *from_path,
 asmlinkage long sys_fsopen(const char __user *fs_name, unsigned int flags);
 asmlinkage long sys_fsmount(int fs_fd, unsigned int flags, unsigned int ms_flags);
 asmlinkage long sys_fspick(int dfd, const char __user *path, unsigned int flags);
+asmlinkage long sys_fsinfo(int dfd, const char __user *path,
+			   struct fsinfo_params __user *params,
+			   void __user *buffer, size_t buf_size);
 
 /*
  * Architecture-specific system calls

@@ -0,0 +1,237 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/* fsinfo() definitions.
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+#ifndef _UAPI_LINUX_FSINFO_H
+#define _UAPI_LINUX_FSINFO_H
+
+#include <linux/types.h>
+#include <linux/socket.h>
+
+/*
+ * The filesystem attributes that can be requested.  Note that some attributes
+ * may have multiple instances which can be switched in the parameter block.
+ */
+enum fsinfo_attribute {
+	fsinfo_attr_statfs		= 0,	/* statfs()-style state */
+	fsinfo_attr_fsinfo		= 1,	/* Information about fsinfo() */
+	fsinfo_attr_ids			= 2,	/* Filesystem IDs */
+	fsinfo_attr_limits		= 3,	/* Filesystem limits */
+	fsinfo_attr_supports		= 4,	/* What's supported in statx, iocflags, ... */
+	fsinfo_attr_capabilities	= 5,	/* Filesystem capabilities (bits) */
+	fsinfo_attr_timestamp_info	= 6,	/* Inode timestamp info */
+	fsinfo_attr_volume_id		= 7,	/* Volume ID (string) */
+	fsinfo_attr_volume_uuid		= 8,	/* Volume UUID (LE uuid) */
+	fsinfo_attr_volume_name		= 9,	/* Volume name (string) */
+	fsinfo_attr_cell_name		= 10,	/* Cell name (string) */
+	fsinfo_attr_domain_name		= 11,	/* Domain name (string) */
+	fsinfo_attr_realm_name		= 12,	/* Realm name (string) */
+	fsinfo_attr_server_name		= 13,	/* Name of the Nth server */
+	fsinfo_attr_server_address	= 14,	/* Mth address of the Nth server */
+	fsinfo_attr_parameter		= 15,	/* Nth mount parameter (string) */
+	fsinfo_attr_source		= 16,	/* Nth mount source name (string) */
+	fsinfo_attr_name_encoding	= 17,	/* Filename encoding (string) */
+	fsinfo_attr_name_codepage	= 18,	/* Filename codepage (string) */
+	fsinfo_attr_io_size		= 19,	/* Optimal I/O sizes */
+	fsinfo_attr__nr
+};
+
+/*
+ * Optional fsinfo() parameter structure.
+ *
+ * If this is not given, it is assumed that fsinfo_attr_statfs instance 0,0 is
+ * desired.
+ */
+struct fsinfo_params {
+	__u32	at_flags;	/* AT_SYMLINK_NOFOLLOW and similar flags */
+	__u32	request;	/* What is being asking for (enum fsinfo_attribute) */
+	__u32	Nth;		/* Instance of it (some may have multiple) */
+	__u32	Mth;		/* Subinstance of Nth instance */
+	__u32	__reserved[6];	/* Reserved params; all must be 0 */
+};
+
+/*
+ * Information struct for fsinfo(fsinfo_attr_statfs).
+ * - This gives extended filesystem information.
+ */
+struct fsinfo_statfs {
+	__u64	f_blocks;	/* Total number of blocks in fs */
+	__u64	f_bfree;	/* Total number of free blocks */
+	__u64	f_bavail;	/* Number of free blocks available to ordinary user */
+	__u64	f_files;	/* Total number of file nodes in fs */
+	__u64	f_ffree;	/* Number of free file nodes */
+	__u64	f_favail;	/* Number of free file nodes available to ordinary user */
+	__u32	f_bsize;	/* Optimal block size */
+	__u32	f_frsize;	/* Fragment size */
+};
+
+/*
+ * Information struct for fsinfo(fsinfo_attr_ids).
+ *
+ * List of basic identifiers as is normally found in statfs().
+ */
+struct fsinfo_ids {
+	char	f_fs_name[15 + 1];
+	__u64	f_flags;	/* Filesystem mount flags (MS_*) */
+	__u64	f_fsid;		/* Short 64-bit Filesystem ID (as statfs) */
+	__u64	f_sb_id;	/* Internal superblock ID for sbnotify()/mntnotify() */
+	__u32	f_fstype;	/* Filesystem type from linux/magic.h [uncond] */
+	__u32	f_dev_major;	/* As st_dev_* from struct statx [uncond] */
+	__u32	f_dev_minor;
+};
+
+/*
+ * Information struct for fsinfo(fsinfo_attr_limits).
+ *
+ * List of supported filesystem limits.
+ */
+struct fsinfo_limits {
+	__u64	max_file_size;			/* Maximum file size */
+	__u64	max_uid;			/* Maximum UID supported */
+	__u64	max_gid;			/* Maximum GID supported */
+	__u64	max_projid;			/* Maximum project ID supported */
+	__u32	max_dev_major;			/* Maximum device major representable */
+	__u32	max_dev_minor;			/* Maximum device minor representable */
+	__u32	max_hard_links;			/* Maximum number of hard links on a file */
+	__u32	max_xattr_body_len;		/* Maximum xattr content length */
+	__u32	max_xattr_name_len;		/* Maximum xattr name length */
+	__u32	max_filename_len;		/* Maximum filename length */
+	__u32	max_symlink_len;		/* Maximum symlink content length */
+	__u32	__reserved[1];
+};
+
+/*
+ * Information struct for fsinfo(fsinfo_attr_supports).
+ *
+ * What's supported in various masks, such as statx() attribute and mask bits
+ * and IOC flags.
+ */
+struct fsinfo_supports {
+	__u64	stx_attributes;		/* What statx::stx_attributes are supported */
+	__u32	stx_mask;		/* What statx::stx_mask bits are supported */
+	__u32	ioc_flags;		/* What FS_IOC_* flags are supported */
+	__u32	win_file_attrs;		/* What DOS/Windows FILE_* attributes are supported */
+	__u32	__reserved[1];
+};
+
+/*
+ * Information struct for fsinfo(fsinfo_attr_capabilities).
+ *
+ * Bitmask indicating filesystem capabilities where renderable as single bits.
+ */
+enum fsinfo_capability {
+	fsinfo_cap_is_kernel_fs		= 0,	/* fs is kernel-special filesystem */
+	fsinfo_cap_is_block_fs		= 1,	/* fs is block-based filesystem */
+	fsinfo_cap_is_flash_fs		= 2,	/* fs is flash filesystem */
+	fsinfo_cap_is_network_fs	= 3,	/* fs is network filesystem */
+	fsinfo_cap_is_automounter_fs	= 4,	/* fs is automounter special filesystem */
+	fsinfo_cap_automounts		= 5,	/* fs supports automounts */
+	fsinfo_cap_adv_locks		= 6,	/* fs supports advisory file locking */
+	fsinfo_cap_mand_locks		= 7,	/* fs supports mandatory file locking */
+	fsinfo_cap_leases		= 8,	/* fs supports file leases */
+	fsinfo_cap_uids			= 9,	/* fs supports numeric uids */
+	fsinfo_cap_gids			= 10,	/* fs supports numeric gids */
+	fsinfo_cap_projids		= 11,	/* fs supports numeric project ids */
+	fsinfo_cap_id_names		= 12,	/* fs supports user names */
+	fsinfo_cap_id_guids		= 13,	/* fs supports user guids */
+	fsinfo_cap_windows_attrs	= 14,	/* fs has windows attributes */
+	fsinfo_cap_user_quotas		= 15,	/* fs has per-user quotas */
+	fsinfo_cap_group_quotas		= 16,	/* fs has per-group quotas */
+	fsinfo_cap_project_quotas	= 17,	/* fs has per-project quotas */
+	fsinfo_cap_xattrs		= 18,	/* fs has xattrs */
+	fsinfo_cap_journal		= 19,	/* fs has a journal */
+	fsinfo_cap_data_is_journalled	= 20,	/* fs is using data journalling */
+	fsinfo_cap_o_sync		= 21,	/* fs supports O_SYNC */
+	fsinfo_cap_o_direct		= 22,	/* fs supports O_DIRECT */
+	fsinfo_cap_volume_id		= 23,	/* fs has a volume ID */
+	fsinfo_cap_volume_uuid		= 24,	/* fs has a volume UUID */
+	fsinfo_cap_volume_name		= 25,	/* fs has a volume name */
+	fsinfo_cap_volume_fsid		= 26,	/* fs has a volume FSID */
+	fsinfo_cap_cell_name		= 27,	/* fs has a cell name */
+	fsinfo_cap_domain_name		= 28,	/* fs has a domain name */
+	fsinfo_cap_realm_name		= 29,	/* fs has a realm name */
+	fsinfo_cap_iver_all_change	= 30,	/* i_version represents data + meta changes */
+	fsinfo_cap_iver_data_change	= 31,	/* i_version represents data changes only */
+	fsinfo_cap_iver_mono_incr	= 32,	/* i_version incremented monotonically */
+	fsinfo_cap_symlinks		= 33,	/* fs supports symlinks */
+	fsinfo_cap_hard_links		= 34,	/* fs supports hard links */
+	fsinfo_cap_hard_links_1dir	= 35,	/* fs supports hard links in same dir only */
+	fsinfo_cap_device_files		= 36,	/* fs supports bdev, cdev */
+	fsinfo_cap_unix_specials	= 37,	/* fs supports pipe, fifo, socket */
+	fsinfo_cap_resource_forks	= 38,	/* fs supports resource forks/streams */
+	fsinfo_cap_name_case_indep	= 39,	/* Filename case independence is mandatory */
+	fsinfo_cap_name_non_utf8	= 40,	/* fs has non-utf8 names */
+	fsinfo_cap_name_has_codepage	= 41,	/* fs has a filename codepage */
+	fsinfo_cap_sparse		= 42,	/* fs supports sparse files */
+	fsinfo_cap_not_persistent	= 43,	/* fs is not persistent */
+	fsinfo_cap_no_unix_mode		= 44,	/* fs does not support unix mode bits */
+	fsinfo_cap_has_atime		= 45,	/* fs supports access time */
+	fsinfo_cap_has_btime		= 46,	/* fs supports birth/creation time */
+	fsinfo_cap_has_ctime		= 47,	/* fs supports change time */
+	fsinfo_cap_has_mtime		= 48,	/* fs supports modification time */
+	fsinfo_cap__nr
+};
+
+struct fsinfo_capabilities {
+	__u8	capabilities[(fsinfo_cap__nr + 7) / 8];
+};
+
+/*
+ * Information struct for fsinfo(fsinfo_attr_timestamp_info).
+ */
+struct fsinfo_timestamp_info {
+	__s64	minimum_timestamp;	/* Minimum timestamp value in seconds */
+	__s64	maximum_timestamp;	/* Maximum timestamp value in seconds */
+	__u16	atime_gran_mantissa;	/* Granularity(secs) = mant * 10^exp */
+	__u16	btime_gran_mantissa;
+	__u16	ctime_gran_mantissa;
+	__u16	mtime_gran_mantissa;
+	__s8	atime_gran_exponent;
+	__s8	btime_gran_exponent;
+	__s8	ctime_gran_exponent;
+	__s8	mtime_gran_exponent;
+	__u32	__reserved[1];
+};
+
+/*
+ * Information struct for fsinfo(fsinfo_attr_volume_uuid).
+ */
+struct fsinfo_volume_uuid {
+	__u8	uuid[16];
+};
+
+/*
+ * Information struct for fsinfo(fsinfo_attr_server_addresses).
+ *
+ * Find the Mth address of the Nth server for a network mount.
+ */
+struct fsinfo_server_address {
+	struct __kernel_sockaddr_storage address;
+};
+
+/*
+ * Information struct for fsinfo(fsinfo_attr_io_size).
+ *
+ * Retrieve the optimal I/O size for a filesystem.
+ */
+struct fsinfo_io_size {
+	__u32		block_size;		/* Minimum block granularity for O_DIRECT */
+	__u32		max_single_read_size;	/* Maximum size of a single unbuffered read */
+	__u32		max_single_write_size;	/* Maximum size of a single unbuffered write */
+	__u32		best_read_size;		/* Optimal read size */
+	__u32		best_write_size;	/* Optimal write size */
+};
+
+/*
+ * Information struct for fsinfo(fsinfo_attr_fsinfo).
+ *
+ * This gives information about fsinfo() itself.
+ */
+struct fsinfo_fsinfo {
+	__u32	max_attr;	/* Number of supported attributes (fsinfo_attr__nr) */
+	__u32	max_cap;	/* Number of supported capabilities (fsinfo_cap__nr) */
+};
+
+#endif /* _UAPI_LINUX_FSINFO_H */

@@ -1,7 +1,10 @@
 # List of programs to build
-hostprogs-$(CONFIG_SAMPLE_STATX) := test-statx
+hostprogs-$(CONFIG_SAMPLE_STATX) := test-statx test-fsinfo
 
 # Tell kbuild to always build the programs
 always := $(hostprogs-y)
 
 HOSTCFLAGS_test-statx.o += -I$(objtree)/usr/include
+
+HOSTCFLAGS_test-fsinfo.o += -I$(objtree)/usr/include
+HOSTLOADLIBES_test-fsinfo += -lm

@@ -0,0 +1,539 @@
+/* Test the fsinfo() system call
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#define _GNU_SOURCE
+#define _ATFILE_SOURCE
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <unistd.h>
+#include <ctype.h>
+#include <errno.h>
+#include <time.h>
+#include <math.h>
+#include <fcntl.h>
+#include <sys/syscall.h>
+#include <linux/fsinfo.h>
+#include <linux/socket.h>
+#include <sys/stat.h>
+
+static __attribute__((unused))
+ssize_t fsinfo(int dfd, const char *filename, struct fsinfo_params *params,
+	       void *buffer, size_t buf_size)
+{
+	return syscall(__NR_fsinfo, dfd, filename, params, buffer, buf_size);
+}
+
+#define FSINFO_STRING(N)	 [fsinfo_attr_##N] = 0x00
+#define FSINFO_STRUCT(N)	 [fsinfo_attr_##N] = sizeof(struct fsinfo_##N)/sizeof(__u32)
+#define FSINFO_STRING_N(N)	 [fsinfo_attr_##N] = 0x40
+#define FSINFO_STRUCT_N(N)	 [fsinfo_attr_##N] = 0x40 | sizeof(struct fsinfo_##N)/sizeof(__u32)
+#define FSINFO_STRUCT_NM(N)	 [fsinfo_attr_##N] = 0x80 | sizeof(struct fsinfo_##N)/sizeof(__u32)
+static const __u8 fsinfo_buffer_sizes[fsinfo_attr__nr] = {
+	FSINFO_STRUCT		(statfs),
+	FSINFO_STRUCT		(fsinfo),
+	FSINFO_STRUCT		(ids),
+	FSINFO_STRUCT		(limits),
+	FSINFO_STRUCT		(supports),
+	FSINFO_STRUCT		(capabilities),
+	FSINFO_STRUCT		(timestamp_info),
+	FSINFO_STRING		(volume_id),
+	FSINFO_STRUCT		(volume_uuid),
+	FSINFO_STRING		(volume_name),
+	FSINFO_STRING		(cell_name),
+	FSINFO_STRING		(domain_name),
+	FSINFO_STRING		(realm_name),
+	FSINFO_STRING_N		(server_name),
+	FSINFO_STRUCT_NM	(server_address),
+	FSINFO_STRING_N		(parameter),
+	FSINFO_STRING_N		(source),
+	FSINFO_STRING		(name_encoding),
+	FSINFO_STRING		(name_codepage),
+	FSINFO_STRUCT		(io_size),
+};
+
+#define FSINFO_NAME(N) [fsinfo_attr_##N] = #N
+static const char *fsinfo_attr_names[fsinfo_attr__nr] = {
+	FSINFO_NAME(statfs),
+	FSINFO_NAME(fsinfo),
+	FSINFO_NAME(ids),
+	FSINFO_NAME(limits),
+	FSINFO_NAME(supports),
+	FSINFO_NAME(capabilities),
+	FSINFO_NAME(timestamp_info),
+	FSINFO_NAME(volume_id),
+	FSINFO_NAME(volume_uuid),
+	FSINFO_NAME(volume_name),
+	FSINFO_NAME(cell_name),
+	FSINFO_NAME(domain_name),
+	FSINFO_NAME(realm_name),
+	FSINFO_NAME(server_name),
+	FSINFO_NAME(server_address),
+	FSINFO_NAME(parameter),
+	FSINFO_NAME(source),
+	FSINFO_NAME(name_encoding),
+	FSINFO_NAME(name_codepage),
+	FSINFO_NAME(io_size),
+};
+
+union reply {
+	char buffer[4096];
+	struct fsinfo_statfs statfs;
+	struct fsinfo_fsinfo fsinfo;
+	struct fsinfo_ids ids;
+	struct fsinfo_limits limits;
+	struct fsinfo_supports supports;
+	struct fsinfo_capabilities caps;
+	struct fsinfo_timestamp_info timestamps;
+	struct fsinfo_volume_uuid uuid;
+	struct fsinfo_server_address srv_addr;
+	struct fsinfo_io_size io_size;
+};
+
+static void dump_hex(unsigned int *data, int from, int to)
+{
+	unsigned offset, print_offset = 1, col = 0;
+
+	from /= 4;
+	to = (to + 3) / 4;
+
+	for (offset = from; offset < to; offset++) {
+		if (print_offset) {
+			printf("%04x: ", offset * 8);
+			print_offset = 0;
+		}
+		printf("%08x", data[offset]);
+		col++;
+		if ((col & 3) == 0) {
+			printf("\n");
+			print_offset = 1;
+		} else {
+			printf(" ");
+		}
+	}
+
+	if (!print_offset)
+		printf("\n");
+}
+
+static void dump_attr_statfs(union reply *r, int size)
+{
+	struct fsinfo_statfs *f = &r->statfs;
+
+	printf("\n");
+	printf("\tblocks: n=%llu fr=%llu av=%llu\n",
+	       (unsigned long long)f->f_blocks,
+	       (unsigned long long)f->f_bfree,
+	       (unsigned long long)f->f_bavail);
+
+	printf("\tfiles : n=%llu fr=%llu av=%llu\n",
+	       (unsigned long long)f->f_files,
+	       (unsigned long long)f->f_ffree,
+	       (unsigned long long)f->f_favail);
+	printf("\tbsize : %u\n", f->f_bsize);
+	printf("\tfrsize: %u\n", f->f_frsize);
+}
+
+static void dump_attr_fsinfo(union reply *r, int size)
+{
+	struct fsinfo_fsinfo *f = &r->fsinfo;
+
+	printf("max_attr=%u max_cap=%u\n", f->max_attr, f->max_cap);
+}
+
+static void dump_attr_ids(union reply *r, int size)
+{
+	struct fsinfo_ids *f = &r->ids;
+
+	printf("\n");
+	printf("\tdev   : %02x:%02x\n", f->f_dev_major, f->f_dev_minor);
+	printf("\tfs    : type=%x name=%s\n", f->f_fstype, f->f_fs_name);
+	printf("\tflags : %llx\n", (unsigned long long)f->f_flags);
+	printf("\tfsid  : %llx\n", (unsigned long long)f->f_fsid);
+}
+
+static void dump_attr_limits(union reply *r, int size)
+{
+	struct fsinfo_limits *f = &r->limits;
+
+	printf("\n");
+	printf("\tmax file size: %llx\n", f->max_file_size);
+	printf("\tmax ids      : u=%llx g=%llx p=%llx\n",
+	       f->max_uid, f->max_gid, f->max_projid);
+	printf("\tmax dev      : maj=%x min=%x\n",
+	       f->max_dev_major, f->max_dev_minor);
+	printf("\tmax links    : %x\n", f->max_hard_links);
+	printf("\tmax xattr    : n=%x b=%x\n",
+	       f->max_xattr_name_len, f->max_xattr_body_len);
+	printf("\tmax len      : file=%x sym=%x\n",
+	       f->max_filename_len, f->max_symlink_len);
+}
+
+static void dump_attr_supports(union reply *r, int size)
+{
+	struct fsinfo_supports *f = &r->supports;
+
+	printf("\n");
+	printf("\tstx_attr=%llx\n", f->stx_attributes);
+	printf("\tstx_mask=%x\n", f->stx_mask);
+	printf("\tioc_flags=%x\n", f->ioc_flags);
+	printf("\twin_fattrs=%x\n", f->win_file_attrs);
+}
+
+#define FSINFO_CAP_NAME(C) [fsinfo_cap_##C] = #C
+static const char *fsinfo_cap_names[fsinfo_cap__nr] = {
+	FSINFO_CAP_NAME(is_kernel_fs),
+	FSINFO_CAP_NAME(is_block_fs),
+	FSINFO_CAP_NAME(is_flash_fs),
+	FSINFO_CAP_NAME(is_network_fs),
+	FSINFO_CAP_NAME(is_automounter_fs),
+	FSINFO_CAP_NAME(automounts),
+	FSINFO_CAP_NAME(adv_locks),
+	FSINFO_CAP_NAME(mand_locks),
+	FSINFO_CAP_NAME(leases),
+	FSINFO_CAP_NAME(uids),
+	FSINFO_CAP_NAME(gids),
+	FSINFO_CAP_NAME(projids),
+	FSINFO_CAP_NAME(id_names),
+	FSINFO_CAP_NAME(id_guids),
+	FSINFO_CAP_NAME(windows_attrs),
+	FSINFO_CAP_NAME(user_quotas),
+	FSINFO_CAP_NAME(group_quotas),
+	FSINFO_CAP_NAME(project_quotas),
+	FSINFO_CAP_NAME(xattrs),
+	FSINFO_CAP_NAME(journal),
+	FSINFO_CAP_NAME(data_is_journalled),
+	FSINFO_CAP_NAME(o_sync),
+	FSINFO_CAP_NAME(o_direct),
+	FSINFO_CAP_NAME(volume_id),
+	FSINFO_CAP_NAME(volume_uuid),
+	FSINFO_CAP_NAME(volume_name),
+	FSINFO_CAP_NAME(volume_fsid),
+	FSINFO_CAP_NAME(cell_name),
+	FSINFO_CAP_NAME(domain_name),
+	FSINFO_CAP_NAME(realm_name),
+	FSINFO_CAP_NAME(iver_all_change),
+	FSINFO_CAP_NAME(iver_data_change),
+	FSINFO_CAP_NAME(iver_mono_incr),
+	FSINFO_CAP_NAME(symlinks),
+	FSINFO_CAP_NAME(hard_links),
+	FSINFO_CAP_NAME(hard_links_1dir),
+	FSINFO_CAP_NAME(device_files),
+	FSINFO_CAP_NAME(unix_specials),
+	FSINFO_CAP_NAME(resource_forks),
+	FSINFO_CAP_NAME(name_case_indep),
+	FSINFO_CAP_NAME(name_non_utf8),
+	FSINFO_CAP_NAME(name_has_codepage),
+	FSINFO_CAP_NAME(sparse),
+	FSINFO_CAP_NAME(not_persistent),
+	FSINFO_CAP_NAME(no_unix_mode),
+	FSINFO_CAP_NAME(has_atime),
+	FSINFO_CAP_NAME(has_btime),
+	FSINFO_CAP_NAME(has_ctime),
+	FSINFO_CAP_NAME(has_mtime),
+};
+
+static void dump_attr_capabilities(union reply *r, int size)
+{
+	struct fsinfo_capabilities *f = &r->caps;
+	int i;
+
+	for (i = 0; i < sizeof(f->capabilities); i++)
+		printf("%02x", f->capabilities[i]);
+	printf("\n");
+	for (i = 0; i < fsinfo_cap__nr; i++)
+		if (f->capabilities[i / 8] & (1 << (i % 8)))
+			printf("\t- %s\n", fsinfo_cap_names[i]);
+}
+
+static void dump_attr_timestamp_info(union reply *r, int size)
+{
+	struct fsinfo_timestamp_info *f = &r->timestamps;
+
+	printf("range=%llx-%llx\n",
+	       (unsigned long long)f->minimum_timestamp,
+	       (unsigned long long)f->maximum_timestamp);
+
+#define print_time(G) \
+	printf("\t"#G"time : gran=%gs\n",			\
+	       (f->G##time_gran_mantissa *		\
+		pow(10., f->G##time_gran_exponent)))
+	print_time(a);
+	print_time(b);
+	print_time(c);
+	print_time(m);
+}
+
+static void dump_attr_volume_uuid(union reply *r, int size)
+{
+	struct fsinfo_volume_uuid *f = &r->uuid;
+
+	printf("%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x"
+	       "-%02x%02x%02x%02x%02x%02x\n",
+	       f->uuid[ 0], f->uuid[ 1],
+	       f->uuid[ 2], f->uuid[ 3],
+	       f->uuid[ 4], f->uuid[ 5],
+	       f->uuid[ 6], f->uuid[ 7],
+	       f->uuid[ 8], f->uuid[ 9],
+	       f->uuid[10], f->uuid[11],
+	       f->uuid[12], f->uuid[13],
+	       f->uuid[14], f->uuid[15]);
+}
+
+static void dump_attr_server_address(union reply *r, int size)
+{
+	struct fsinfo_server_address *f = &r->srv_addr;
+
+	printf("family=%u\n", f->address.ss_family);
+}
+
+static void dump_attr_io_size(union reply *r, int size)
+{
+	struct fsinfo_io_size *f = &r->io_size;
+
+	printf("bs=%u\n", f->block_size);
+}
+
+/*
+ *
+ */
+typedef void (*dumper_t)(union reply *r, int size);
+
+#define FSINFO_DUMPER(N) [fsinfo_attr_##N] = dump_attr_##N
+static const dumper_t fsinfo_attr_dumper[fsinfo_attr__nr] = {
+	FSINFO_DUMPER(statfs),
+	FSINFO_DUMPER(fsinfo),
+	FSINFO_DUMPER(ids),
+	FSINFO_DUMPER(limits),
+	FSINFO_DUMPER(supports),
+	FSINFO_DUMPER(capabilities),
+	FSINFO_DUMPER(timestamp_info),
+	FSINFO_DUMPER(volume_uuid),
+	FSINFO_DUMPER(server_address),
+	FSINFO_DUMPER(io_size),
+};
+
+static void dump_fsinfo(enum fsinfo_attribute attr, __u8 about,
+			union reply *r, int size)
+{
+	dumper_t dumper = fsinfo_attr_dumper[attr];
+	unsigned int len;
+
+	if (!dumper) {
+		printf("<no dumper>\n");
+		return;
+	}
+
+	len = (about & 0x3f) * sizeof(__u32);
+	if (size < len) {
+		printf("<short data %u/%u>\n", size, len);
+		return;
+	}
+
+	dumper(r, size);
+}
+
+/*
+ * Try one subinstance of an attribute.
+ */
+static int try_one(const char *file, struct fsinfo_params *params, bool raw)
+{
+	union reply r;
+	char *p;
+	int ret;
+	__u8 about;
+
+	memset(&r.buffer, 0xbd, sizeof(r.buffer));
+
+	errno = 0;
+	ret = fsinfo(AT_FDCWD, file, params, r.buffer, sizeof(r.buffer));
+	if (params->request >= fsinfo_attr__nr) {
+		if (ret == -1 && errno == EOPNOTSUPP)
+			exit(0);
+		fprintf(stderr, "Unexpected error for too-large command %u: %m\n",
+			params->request);
+		exit(1);
+	}
+
+	//printf("fsinfo(%s,%s,%u,%u) = %d: %m\n",
+	//       file, fsinfo_attr_names[params->request],
+	//       params->Nth, params->Mth, ret);
+
+	about = fsinfo_buffer_sizes[params->request];
+	if (ret == -1) {
+		if (errno == ENODATA) {
+			switch (about & 0xc0) {
+			case 0x00:
+				if (params->Nth == 0 && params->Mth == 0) {
+					fprintf(stderr,
+						"Unexpected ENODATA1 (%u[%u][%u])\n",
+						params->request, params->Nth, params->Mth);
+					exit(1);
+				}
+				break;
+			case 0x40:
+				if (params->Nth == 0 && params->Mth == 0) {
+					fprintf(stderr,
+						"Unexpected ENODATA2 (%u[%u][%u])\n",
+						params->request, params->Nth, params->Mth);
+					exit(1);
+				}
+				break;
+			}
+			return (params->Mth == 0) ? 2 : 1;
+		}
+		if (errno == EOPNOTSUPP) {
+			if (params->Nth > 0 || params->Mth > 0) {
+				fprintf(stderr,
+					"Should return -ENODATA (%u[%u][%u])\n",
+					params->request, params->Nth, params->Mth);
+				exit(1);
+			}
+			//printf("\e[33m%s\e[m: <not supported>\n",
+			//       fsinfo_attr_names[attr]);
+			return 2;
+		}
+		perror(file);
+		exit(1);
+	}
+
+	if (raw) {
+		if (ret > 4096)
+			ret = 4096;
+		dump_hex((unsigned int *)&r.buffer, 0, ret);
+		return 0;
+	}
+
+	switch (about & 0xc0) {
+	case 0x00:
+		printf("\e[33m%s\e[m: ",
+		       fsinfo_attr_names[params->request]);
+		break;
+	case 0x40:
+		printf("\e[33m%s[%u]\e[m: ",
+		       fsinfo_attr_names[params->request],
+		       params->Nth);
+		break;
+	case 0x80:
+		printf("\e[33m%s[%u][%u]\e[m: ",
+		       fsinfo_attr_names[params->request],
+		       params->Nth, params->Mth);
+		break;
+	}
+
+	switch (about) {
+		/* Struct */
+	case 0x01 ... 0x3f:
+	case 0x41 ... 0x7f:
+	case 0x81 ... 0xbf:
+		dump_fsinfo(params->request, about, &r, ret);
+		return 0;
+
+		/* String */
+	case 0x00:
+	case 0x40:
+	case 0x80:
+		if (ret >= 4096) {
+			ret = 4096;
+			r.buffer[4092] = '.';
+			r.buffer[4093] = '.';
+			r.buffer[4094] = '.';
+			r.buffer[4095] = 0;
+		} else {
+			r.buffer[ret] = 0;
+		}
+		for (p = r.buffer; *p; p++) {
+			if (!isprint(*p)) {
+				printf("<non-printable>\n");
+				continue;
+			}
+		}
+		printf("%s\n", r.buffer);
+		return 0;
+
+	default:
+		fprintf(stderr, "Fishy about %u %02x\n", params->request, about);
+		exit(1);
+	}
+}
+
+/*
+ *
+ */
+int main(int argc, char **argv)
+{
+	struct fsinfo_params params = {
+		.at_flags = AT_SYMLINK_NOFOLLOW,
+	};
+	unsigned int attr;
+	int raw = 0, opt, Nth, Mth;
+
+	while ((opt = getopt(argc, argv, "alr"))) {
+		switch (opt) {
+		case 'a':
+			params.at_flags |= AT_NO_AUTOMOUNT;
+			continue;
+		case 'l':
+			params.at_flags &= ~AT_SYMLINK_NOFOLLOW;
+			continue;
+		case 'r':
+			raw = 1;
+			continue;
+		}
+		break;
+	}
+
+	argc -= optind;
+	argv += optind;
+
+	if (argc != 1) {
+		printf("Format: test-fsinfo [-alr] <file>\n");
+		exit(2);
+	}
+
+	for (attr = 0; attr <= fsinfo_attr__nr; attr++) {
+		Nth = 0;
+		do {
+			Mth = 0;
+			do {
+				params.request = attr;
+				params.Nth = Nth;
+				params.Mth = Mth;
+
+				switch (try_one(argv[0], &params, raw)) {
+				case 0:
+					continue;
+				case 1:
+					goto done_M;
+				case 2:
+					goto done_N;
+				}
+			} while (++Mth < 100);
+
+		done_M:
+			if (Mth >= 100) {
+				fprintf(stderr, "Fishy: Mth == %u\n", Mth);
+				break;
+			}
+
+		} while (++Nth < 100);
+
+	done_N:
+		if (Nth >= 100) {
+			fprintf(stderr, "Fishy: Nth == %u\n", Nth);
+			break;
+		}
+	}
+
+	return 0;
+}