Re: [PATCH 01/11] vfs: syscall: Add fsinfo() to query filesystem information [ver #15]

Add a system call to allow filesystem information to be queried.  A request
value can be given to indicate the desired attribute.  Support is provided
for enumerating multi-value attributes.

===============
NEW SYSTEM CALL
===============

The new system call looks like:

	int ret = fsinfo(int dfd,
			 const char *filename,
			 const struct fsinfo_params *params,
			 void *buffer,
			 size_t buf_size);

The params parameter optionally points to a block of parameters:

	struct fsinfo_params {
		__u32	at_flags;
		__u32	request;
		__u32	Nth;
		__u32	Mth;
		__u64	__reserved[3];
	};

If params is NULL, it is assumed params->request should be
fsinfo_attr_statfs, params->Nth should be 0, params->Mth should be 0 and
params->at_flags should be 0.

If params is given, all of params->__reserved[] must be 0.

dfd, filename and params->at_flags indicate the file to query.  There is no
equivalent of lstat() as that can be emulated with fsinfo() by setting
AT_SYMLINK_NOFOLLOW in params->at_flags.  There is also no equivalent of
fstat() as that can be emulated by passing a NULL filename to fsinfo() with
the fd of interest in dfd.  AT_NO_AUTOMOUNT can also be used to an allow
automount point to be queried without triggering it.

params->request indicates the attribute/attributes to be queried.  This can
be one of:

	FSINFO_ATTR_STATFS		- statfs-style info
	FSINFO_ATTR_FSINFO		- Information about fsinfo()
	FSINFO_ATTR_IDS			- Filesystem IDs
	FSINFO_ATTR_LIMITS		- Filesystem limits
	FSINFO_ATTR_SUPPORTS		- What's supported in statx(), IOC flags
	FSINFO_ATTR_CAPABILITIES	- Filesystem capabilities
	FSINFO_ATTR_TIMESTAMP_INFO	- Inode timestamp info
	FSINFO_ATTR_VOLUME_ID		- Volume ID (string)
	FSINFO_ATTR_VOLUME_UUID		- Volume UUID
	FSINFO_ATTR_VOLUME_NAME		- Volume name (string)
	FSINFO_ATTR_NAME_ENCODING	- Filename encoding (string)
	FSINFO_ATTR_NAME_CODEPAGE	- Filename codepage (string)

Some attributes (such as the servers backing a network filesystem) can have
multiple values.  These can be enumerated by setting params->Nth and
params->Mth to 0, 1, ... until ENODATA is returned.

buffer and buf_size point to the reply buffer.  The buffer is filled up to
the specified size, even if this means truncating the reply.  The full size
of the reply is returned.  In future versions, this will allow extra fields
to be tacked on to the end of the reply, but anyone not expecting them will
only get the subset they're expecting.  If either buffer of buf_size are 0,
no copy will take place and the data size will be returned.

At the moment, this will only work on x86_64 and i386 as it requires the
system call to be wired up.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-api@vger.kernel.org
---

 arch/x86/entry/syscalls/syscall_32.tbl |    1 
 arch/x86/entry/syscalls/syscall_64.tbl |    1 
 fs/Kconfig                             |    7 
 fs/Makefile                            |    1 
 fs/fsinfo.c                            |  545 ++++++++++++++++++++++++++++++++
 include/linux/fs.h                     |    5 
 include/linux/fsinfo.h                 |   65 ++++
 include/linux/syscalls.h               |    4 
 include/uapi/asm-generic/unistd.h      |    4 
 include/uapi/linux/fsinfo.h            |  219 +++++++++++++
 kernel/sys_ni.c                        |    1 
 samples/vfs/Makefile                   |    4 
 samples/vfs/test-fsinfo.c              |  551 ++++++++++++++++++++++++++++++++
 13 files changed, 1407 insertions(+), 1 deletion(-)
 create mode 100644 fs/fsinfo.c
 create mode 100644 include/linux/fsinfo.h
 create mode 100644 include/uapi/linux/fsinfo.h
 create mode 100644 samples/vfs/test-fsinfo.c

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index ad968b7bac72..03decae51513 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl

@@ -438,3 +438,4 @@
 431	i386	fsconfig		sys_fsconfig			__ia32_sys_fsconfig
 432	i386	fsmount			sys_fsmount			__ia32_sys_fsmount
 433	i386	fspick			sys_fspick			__ia32_sys_fspick
+434	i386	fsinfo			sys_fsinfo			__ia32_sys_fsinfo

diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index b4e6f9e6204a..ea63df9a1020 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl

@@ -355,6 +355,7 @@
 431	common	fsconfig		__x64_sys_fsconfig
 432	common	fsmount			__x64_sys_fsmount
 433	common	fspick			__x64_sys_fspick
+434	common	fsinfo			__x64_sys_fsinfo
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact

diff --git a/fs/Kconfig b/fs/Kconfig
index cbbffc8b9ef5..9e7d2f2c0111 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig

@@ -15,6 +15,13 @@ config VALIDATE_FS_PARSER
 	  Enable this to perform validation of the parameter description for a
 	  filesystem when it is registered.
 
+config FSINFO
+	bool "Enable the fsinfo() system call"
+	help
+	  Enable the file system information querying system call to allow
+	  comprehensive information to be retrieved about a filesystem,
+	  superblock or mount object.
+
 if BLOCK
 
 config FS_IOMAP

diff --git a/fs/Makefile b/fs/Makefile
index c9aea23aba56..26eaeae4b9a1 100644
--- a/fs/Makefile
+++ b/fs/Makefile

@@ -53,6 +53,7 @@ obj-$(CONFIG_SYSCTL)		+= drop_caches.o
 
 obj-$(CONFIG_FHANDLE)		+= fhandle.o
 obj-$(CONFIG_FS_IOMAP)		+= iomap.o
+obj-$(CONFIG_FSINFO)		+= fsinfo.o
 
 obj-y				+= quota/
 

diff --git a/fs/fsinfo.c b/fs/fsinfo.c
new file mode 100644
index 000000000000..09e743b16235
--- /dev/null
+++ b/fs/fsinfo.c

@@ -0,0 +1,545 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Filesystem information query.
+ *
+ * Copyright (C) 2019 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+#include <linux/syscalls.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/statfs.h>
+#include <linux/security.h>
+#include <linux/uaccess.h>
+#include <linux/fsinfo.h>
+#include <uapi/linux/mount.h>
+#include "internal.h"
+
+static u32 calc_mount_attrs(u32 mnt_flags)

+{
+	u32 attrs = 0;
+
+	if (mnt_flags & MNT_READONLY)
+		attrs |= MOUNT_ATTR_RDONLY;
+	if (mnt_flags & MNT_NOSUID)
+		attrs |= MOUNT_ATTR_NOSUID;
+	if (mnt_flags & MNT_NODEV)
+		attrs |= MOUNT_ATTR_NODEV;
+	if (mnt_flags & MNT_NOEXEC)
+		attrs |= MOUNT_ATTR_NOEXEC;
+	if (mnt_flags & MNT_NODIRATIME)
+		attrs |= MOUNT_ATTR_NODIRATIME;
+
+	if (mnt_flags & MNT_NOATIME)
+		attrs |= MOUNT_ATTR_NOATIME;
+	else if (mnt_flags & MNT_RELATIME)
+		attrs |= MOUNT_ATTR_RELATIME;
+	else
+		attrs |= MOUNT_ATTR_STRICTATIME;
+	return attrs;
+}