Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available [ver #3]

[Andreas Dilger]

On Nov 23, 2016, at 1:37 AM, Michael Kerrisk <mtk.manpages@xxxxxxxxx> wrote:
> 
> Hi David,
> 
> On 11/23/2016 01:55 AM, David Howells wrote:
>> Add a system call to make extended file information available, including
>> file creation and some attribute flags where available through the
>> underlying filesystem.
>> 
>> 
>> ========
>> OVERVIEW
>> ========
>> 
>> The idea was initially proposed as a set of xattrs that could be retrieved
>> with getxattr(), but the general preferance proved to be for a new syscall
> 
> s/preferance/preference/
> 
>> with an extended stat structure.
>> 
>> This can feasibly be used to support a number of things, not all of which
>> are added here:
> 
> It would be very useful if this overview distinguishes which of the features
> below are supported in the initial implementation, versus which features
> (e.g., femtosecond timestamps) are simply allowed for in a future
> implementation.
> 
>> (1) Better support for the y2038 problem [Arnd Bergmann].
>> 
>> (2) Creation time: The SMB protocol carries the creation time, which could
>>     be exported by Samba, which will in turn help CIFS make use of
>>     FS-Cache as that can be used for coherency data.
>> 
>>     This is also specified in NFSv4 as a recommended attribute and could
>>     be exported by NFSD [Steve French].
>> 
>> (3) Lightweight stat: Ask for just those details of interest, and allow a
>>     netfs (such as NFS) to approximate anything not of interest, possibly
>>     without going to the server [Trond Myklebust, Ulrich Drepper, Andreas
>>     Dilger].
>> 
>> (4) Heavyweight stat: Force a netfs to go to the server, even if it thinks
>>     its cached attributes are up to date [Trond Myklebust].
>> 
>> (5) Data version number: Could be used by userspace NFS servers [Aneesh
>>     Kumar].
>> 
>>     Can also be used to modify fill_post_wcc() in NFSD which retrieves
>>     i_version directly, but has just called vfs_getattr().  It could get
>>     it from the kstat struct if it used vfs_xgetattr() instead.
>> 
>> (6) BSD stat compatibility: Including more fields from the BSD stat such
>>     as creation time (st_btime) and inode generation number (st_gen)
>>     [Jeremy Allison, Bernd Schubert].
>> 
>> (7) Inode generation number: Useful for FUSE and userspace NFS servers
>>     [Bernd Schubert].  This was asked for but later deemed unnecessary
>>     with the open-by-handle capability available
>> 
>> (8) Extra coherency data may be useful in making backups [Andreas Dilger].
> 
> Can you elaborate on the point [8] in this commit message. It's not clear
> to me at least what this is about.

To be honest, I'm not even sure what this means, and I've looked through
a few years of different threads trying to find what I suggested that
lead to this entry (looks like statx was first posted on June 29, 2010)
and this entry first appeared in v6 of the patch on July 14, 2010.  The
only comment that seems related is:

https://www.spinics.net/lists/linux-fsdevel/msg33884.html

where I was just pointing out that i_version is updated for regular files,
which is really the same as #5 above. I'm fine with removing it.

Cheers, Andreas

>> 
>> (9) Allow the filesystem to indicate what it can/cannot provide: A
>>     filesystem can now say it doesn't support a standard stat feature if
>>     that isn't available, so if, for instance, inode numbers or UIDs don't
>>     exist or are fabricated locally...
>> 
>> (10) Make the fields a consistent size on all arches and make them large.
>> 
>> (11) Store a 16-byte volume ID in the superblock that can be returned in
>>     struct xstat [Steve French].
>> 
>> (12) Include granularity fields in the time data to indicate the
>>     granularity of each of the times (NFSv4 time_delta) [Steve French].
>> 
>> (13) FS_IOC_GETFLAGS value.  These could be translated to BSD's st_flags.
>>     Note that the Linux IOC flags are a mess and filesystems such as Ext4
>>     define flags that aren't in linux/fs.h, so translation in the kernel
>>     may be a necessity (or, possibly, we provide the filesystem type too).
>> 
>> (14) Mask of features available on file (eg: ACLs, seclabel) [Brad Boyer,
>>     Michael Kerrisk].
>> 
>> (15) Spare space, request flags and information flags are provided for
>>     future expansion.
>> 
>> (16) Femtosecond-resolution timestamps [Dave Chinner].
>> 
>> 
>> ===============
>> NEW SYSTEM CALL
>> ===============
>> 
>> The new system call is:
>> 
>> 	int ret = statx(int dfd,
>> 			const char *filename,
>> 			unsigned int flags,
> 
> In the 0/4 of this patch series, this argument is called 'atflags'.
> These should be consistent. 'flags' seems correct to me.
> 
>> 			unsigned int mask,
>> 			struct statx *buffer);
>> 
>> The dfd, filename and flags parameters indicate the file to query, in a
>> similar way to fstatat().  There is no equivalent of lstat() as that can be
>> emulated with statx() by passing AT_SYMLINK_NOFOLLOW in flags.  There is
>> also no equivalent of fstat() as that can be emulated by passing a NULL
>> filename to statx() with the fd of interest in dfd.
>> 
>> Whether or not statx() synchronises the attributes with the backing store
>> can be controlled (this typically only affects network filesystems) can be
>> set by OR'ing a value into the flags argument:
> 
> s/can be set//
> 
>> 
>> (1) AT_STATX_SYNC_AS_STAT tells statx() to behave as stat() does in this
>>     respect.
>> 
>> (2) AT_STATX_FORCE_SYNC will require a network filesystem to synchronise
>>     its attributes with the server - which might require data writeback to
>>     occur to get the timestamps correct.
>> 
>> (3) AT_STATX_DONT_SYNC will suppress synchronisation with the server in a
>>     network filesystem.  The resulting values should be considered
>>     approximate.
>> 
>> mask is a bitmask indicating the fields in struct statx that are of
>> interest to the caller.  The user should set this to STATX_BASIC_STATS to
>> get the basic set returned by stat().  It should be note that asking for
> 
> s/note/noted/
> 
>> more information may entail extra I/O operations.
>> 
>> buffer points to the destination for the data.  This must be 256 bytes in
>> size.
>> 
>> 
>> ======================
>> MAIN ATTRIBUTES RECORD
>> ======================
>> 
>> The following structures are defined in which to return the main attribute
>> set:
>> 
>> 	struct statx_timestamp {
>> 		__s64	tv_sec;
>> 		__s32	tv_nsec;
>> 		__s32	__reserved;
>> 	};
>> 
>> 	struct statx {
>> 		__u32	stx_mask;
>> 		__u32	stx_blksize;
>> 		__u64	stx_attributes;
>> 		__u32	stx_nlink;
>> 		__u32	stx_uid;
>> 		__u32	stx_gid;
>> 		__u16	stx_mode;
>> 		__u16	__spare0[1];
>> 		__u64	stx_ino;
>> 		__u64	stx_size;
>> 		__u64	stx_blocks;
>> 		__u64	__spare1[1];
>> 		struct statx_timestamp	stx_atime;
>> 		struct statx_timestamp	stx_btime;
>> 		struct statx_timestamp	stx_ctime;
>> 		struct statx_timestamp	stx_mtime;
>> 		__u32	stx_rdev_major;
>> 		__u32	stx_rdev_minor;
>> 		__u32	stx_dev_major;
>> 		__u32	stx_dev_minor;
>> 		__u64	__spare2[14];
>> 	};
>> 
>> The defined bits in request_mask and stx_mask are:
>> 
>> 	STATX_TYPE		Want/got stx_mode & S_IFMT
>> 	STATX_MODE		Want/got stx_mode & ~S_IFMT
>> 	STATX_NLINK		Want/got stx_nlink
>> 	STATX_UID		Want/got stx_uid
>> 	STATX_GID		Want/got stx_gid
>> 	STATX_ATIME		Want/got stx_atime{,_ns}
>> 	STATX_MTIME		Want/got stx_mtime{,_ns}
>> 	STATX_CTIME		Want/got stx_ctime{,_ns}
>> 	STATX_INO		Want/got stx_ino
>> 	STATX_SIZE		Want/got stx_size
>> 	STATX_BLOCKS		Want/got stx_blocks
>> 	STATX_BASIC_STATS	[The stuff in the normal stat struct]
>> 	STATX_BTIME		Want/got stx_btime{,_ns}
>> 	STATX_ALL		[All currently available stuff]
>> 
>> stx_btime is the file creation time, stx_mask is a bitmask indicating the
>> data provided and __spares*[] are where as-yet undefined fields can be
>> placed.
>> 
>> Time fields are structures with separate seconds and nanoseconds fields
>> plus a reserved field in case we want to add even finer resolution.  Note
>> that times will be negative if before 1970; in such a case, the nanosecond
>> fields will also be negative if not zero.
>> 
>> The bits defined in the stx_attributes field convey information about a
>> file, how it is accessed, where it is and what it does.  The following
>> attributes map to FS_*_FL flags and are the same numerical value:
>> 
>> 	STATX_ATTR_COMPRESSED		File is compressed by the fs
>> 	STATX_ATTR_IMMUTABLE		File is marked immutable
>> 	STATX_ATTR_APPEND		File is append-only
>> 	STATX_ATTR_NODUMP		File is not to be dumped
>> 	STATX_ATTR_ENCRYPTED		File requires key to decrypt in fs
>> 
>> Within the kernel, the supported flags are listed by:
>> 
>> 	KSTAT_ATTR_FS_IOC_FLAGS
>> 
>> [Are any other IOC flags of sufficient general interest to be exposed
>> through this interface?]
>> 
>> New flags include:
>> 
>> 	STATX_ATTR_AUTOMOUNT		Object is an automount trigger
>> 
>> These are for the use of GUI tools that might want to mark files specially,
>> depending on what they are.
>> 
>> Fields in struct statx come in a number of classes:
>> 
>> (0) stx_dev_*, stx_blksize.
>> 
>>     These are local system information and are always available.
>> 
>> (1) stx_mode, stx_nlinks, stx_uid, stx_gid, stx_[amc]time, stx_ino,
>>     stx_size, stx_blocks.
>> 
>>     These will be returned whether the caller asks for them or not.  The
>>     corresponding bits in stx_mask will be set to indicate whether they
>>     actually have valid values.
>> 
>>     If the caller didn't ask for them, then they may be approximated.  For
>>     example, NFS won't waste any time updating them from the server,
>>     unless as a byproduct of updating something requested.
>> 
>>     If the values don't actually exist for the underlying object (such as
>>     UID or GID on a DOS file), then the bit won't be set in the stx_mask,
>>     even if the caller asked for the value.  In such a case, the returned
>>     value will be a fabrication.
>> 
>>     Note that there are instances where the type might not be valid, for
>>     instance Windows reparse points.
>> 
>> (2) stx_rdev_*.
>> 
>>     This will be set only if stx_mode indicates we're looking at a
>>     blockdev or a chardev, otherwise will be 0.
>> 
>> (3) stx_btime.
>> 
>>     Similar to (1), except this will be set to 0 if it doesn't exist.
>> 
>> 
>> =======
>> TESTING
>> =======
>> 
>> The following test program can be used to test the statx system call:
>> 
>> 	samples/statx/test-statx.c
>> 
>> Just compile and run, passing it paths to the files you want to examine.
>> The file is built automatically if CONFIG_SAMPLES is enabled.
>> 
>> Here's some example output.  Firstly, an NFS directory that crosses to
>> another FSID.  Note that the AUTOMOUNT attribute is set because transiting
>> this directory will cause d_automount to be invoked by the VFS.
>> 
>> 	[root@andromeda tmp]# ./samples/statx/test-statx -A /warthog/data
>> 	statx(/warthog/data) = 0
>> 	results=17ff
>> 	  Size: 4096            Blocks: 8          IO Block: 1048576  directory
>> 	Device: 00:26           Inode: 1703937     Links: 124
>> 	Access: (3777/drwxrwxrwx)  Uid:     0   Gid:  4041
>> 	Access: 2016-11-10 15:52:11.219935864+0000
>> 	Modify: 2016-11-10 08:07:32.482314928+0000
>> 	Change: 2016-11-10 08:07:32.482314928+0000
>> 	Attributes: 0000000000001000 (-------- -------- -------- -------- -------- -------- ---m---- --------)
>> 	IO-blocksize: blksize=1048576
>> 
>> Secondly, the result of automounting on that directory.
>> 
>> 	[root@andromeda tmp]# ./samples/statx/test-statx /warthog/data
>> 	statx(/warthog/data) = 0
>> 	results=17ff
>> 	  Size: 4096            Blocks: 8          IO Block: 1048576  directory
>> 	Device: 00:27           Inode: 2           Links: 124
>> 	Access: (3777/drwxrwxrwx)  Uid:     0   Gid:  4041
>> 	Access: 2016-11-10 15:52:11.219935864+0000
>> 	Modify: 2016-11-10 08:07:32.482314928+0000
>> 	Change: 2016-11-10 08:07:32.482314928+0000
>> 	IO-blocksize: blksize=1048576
>> 
>> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
>> ---
>> 
>> arch/x86/entry/syscalls/syscall_32.tbl |    1
>> arch/x86/entry/syscalls/syscall_64.tbl |    1
>> fs/exportfs/expfs.c                    |    4
>> fs/stat.c                              |  297 +++++++++++++++++++++++++++++---
>> include/linux/fs.h                     |    5 -
>> include/linux/stat.h                   |   19 +-
>> include/linux/syscalls.h               |    3
>> include/uapi/linux/fcntl.h             |    5 +
>> include/uapi/linux/stat.h              |  120 +++++++++++++
>> samples/Kconfig                        |    5 +
>> samples/Makefile                       |    3
>> samples/statx/Makefile                 |   10 +
>> samples/statx/test-statx.c             |  248 +++++++++++++++++++++++++++
>> 13 files changed, 681 insertions(+), 40 deletions(-)
>> create mode 100644 samples/statx/Makefile
>> create mode 100644 samples/statx/test-statx.c
>> 
>> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
>> index 2b3618542544..9ba050fe47f3 100644
>> --- a/arch/x86/entry/syscalls/syscall_32.tbl
>> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
>> @@ -389,3 +389,4 @@
>> 380	i386	pkey_mprotect		sys_pkey_mprotect
>> 381	i386	pkey_alloc		sys_pkey_alloc
>> 382	i386	pkey_free		sys_pkey_free
>> +383	i386	statx			sys_statx
>> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
>> index e93ef0b38db8..5aef183e2f85 100644
>> --- a/arch/x86/entry/syscalls/syscall_64.tbl
>> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
>> @@ -338,6 +338,7 @@
>> 329	common	pkey_mprotect		sys_pkey_mprotect
>> 330	common	pkey_alloc		sys_pkey_alloc
>> 331	common	pkey_free		sys_pkey_free
>> +332	common	statx			sys_statx
>> 
>> #
>> # x32-specific system call numbers start at 512 to avoid cache impact
>> diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
>> index a4b531be9168..2acc31751248 100644
>> --- a/fs/exportfs/expfs.c
>> +++ b/fs/exportfs/expfs.c
>> @@ -299,7 +299,9 @@ static int get_name(const struct path *path, char *name, struct dentry *child)
>> 	 * filesystem supports 64-bit inode numbers.  So we need to
>> 	 * actually call ->getattr, not just read i_ino:
>> 	 */
>> -	error = vfs_getattr_nosec(&child_path, &stat);
>> +	stat.query_flags = 0;
>> +	stat.request_mask = STATX_BASIC_STATS;
>> +	error = vfs_xgetattr_nosec(&child_path, &stat);
>> 	if (error)
>> 		return error;
>> 	buffer.ino = stat.ino;
>> diff --git a/fs/stat.c b/fs/stat.c
>> index bc045c7994e1..82e656c42157 100644
>> --- a/fs/stat.c
>> +++ b/fs/stat.c
>> @@ -18,6 +18,15 @@
>> #include <asm/uaccess.h>
>> #include <asm/unistd.h>
>> 
>> +/**
>> + * generic_fillattr - Fill in the basic attributes from the inode struct
>> + * @inode: Inode to use as the source
>> + * @stat: Where to fill in the attributes
>> + *
>> + * Fill in the basic attributes in the kstat structure from data that's to be
>> + * found on the VFS inode structure.  This is the default if no getattr inode
>> + * operation is supplied.
>> + */
>> void generic_fillattr(struct inode *inode, struct kstat *stat)
>> {
>> 	stat->dev = inode->i_sb->s_dev;
>> @@ -27,87 +36,189 @@ void generic_fillattr(struct inode *inode, struct kstat *stat)
>> 	stat->uid = inode->i_uid;
>> 	stat->gid = inode->i_gid;
>> 	stat->rdev = inode->i_rdev;
>> -	stat->size = i_size_read(inode);
>> -	stat->atime = inode->i_atime;
>> 	stat->mtime = inode->i_mtime;
>> 	stat->ctime = inode->i_ctime;
>> -	stat->blksize = (1 << inode->i_blkbits);
>> +	stat->size = i_size_read(inode);
>> 	stat->blocks = inode->i_blocks;
>> -}
>> +	stat->blksize = 1 << inode->i_blkbits;
>> 
>> +	stat->result_mask |= STATX_BASIC_STATS;
>> +	if (IS_NOATIME(inode))
>> +		stat->result_mask &= ~STATX_ATIME;
>> +	else
>> +		stat->atime = inode->i_atime;
>> +
>> +	if (IS_AUTOMOUNT(inode))
>> +		stat->attributes |= STATX_ATTR_AUTOMOUNT;
>> +}
>> EXPORT_SYMBOL(generic_fillattr);
>> 
>> /**
>> - * vfs_getattr_nosec - getattr without security checks
>> + * vfs_xgetattr_nosec - getattr without security checks
>>  * @path: file to get attributes from
>>  * @stat: structure to return attributes in
>>  *
>>  * Get attributes without calling security_inode_getattr.
>>  *
>> - * Currently the only caller other than vfs_getattr is internal to the
>> - * filehandle lookup code, which uses only the inode number and returns
>> - * no attributes to any user.  Any other code probably wants
>> - * vfs_getattr.
>> + * Currently the only caller other than vfs_xgetattr is internal to the
>> + * filehandle lookup code, which uses only the inode number and returns no
>> + * attributes to any user.  Any other code probably wants vfs_xgetattr.
>> + *
>> + * The caller must set stat->request_mask to indicate what they want and
>> + * stat->query_flags to indicate whether the server should be queried.
>>  */
>> -int vfs_getattr_nosec(struct path *path, struct kstat *stat)
>> +int vfs_xgetattr_nosec(struct path *path, struct kstat *stat)
>> {
>> 	struct inode *inode = d_backing_inode(path->dentry);
>> 
>> +	stat->query_flags &= ~KSTAT_QUERY_FLAGS;
>> +
>> +	stat->result_mask = 0;
>> +	stat->attributes = 0;
>> 	if (inode->i_op->getattr)
>> 		return inode->i_op->getattr(path->mnt, path->dentry, stat);
>> 
>> 	generic_fillattr(inode, stat);
>> 	return 0;
>> }
>> +EXPORT_SYMBOL(vfs_xgetattr_nosec);
>> 
>> -EXPORT_SYMBOL(vfs_getattr_nosec);
>> -
>> -int vfs_getattr(struct path *path, struct kstat *stat)
>> +/*
>> + * vfs_xgetattr - Get the enhanced basic attributes of a file
>> + * @path: The file of interest
>> + * @stat: Where to return the statistics
>> + *
>> + * Ask the filesystem for a file's attributes.  The caller must have preset
>> + * stat->request_mask and stat->query_flags to indicate what they want.
>> + *
>> + * If the file is remote, the filesystem can be forced to update the attributes
>> + * from the backing store by passing AT_FORCE_ATTR_SYNC in query_flags or can
>> + * suppress the update by passing AT_NO_ATTR_SYNC.
>> + *
>> + * Bits must have been set in stat->request_mask to indicate which attributes
>> + * the caller wants retrieving.  Any such attribute not requested may be
>> + * returned anyway, but the value may be approximate, and, if remote, may not
>> + * have been synchronised with the server.
>> + *
>> + * 0 will be returned on success, and a -ve error code if unsuccessful.
>> + */
>> +int vfs_xgetattr(struct path *path, struct kstat *stat)
>> {
>> 	int retval;
>> 
>> 	retval = security_inode_getattr(path);
>> 	if (retval)
>> 		return retval;
>> -	return vfs_getattr_nosec(path, stat);
>> +	return vfs_xgetattr_nosec(path, stat);
>> }
>> +EXPORT_SYMBOL(vfs_xgetattr);
>> 
>> +/**
>> + * vfs_getattr - Get the basic attributes of a file
>> + * @path: The file of interest
>> + * @stat: Where to return the statistics
>> + *
>> + * Ask the filesystem for a file's attributes.  If remote, the filesystem isn't
>> + * forced to update its files from the backing store.  Only the basic set of
>> + * attributes will be retrieved; anyone wanting more must use vfs_xgetattr(),
>> + * as must anyone who wants to force attributes to be sync'd with the server.
>> + *
>> + * 0 will be returned on success, and a -ve error code if unsuccessful.
>> + */
>> +int vfs_getattr(struct path *path, struct kstat *stat)
>> +{
>> +	stat->query_flags = 0;
>> +	stat->request_mask = STATX_BASIC_STATS;
>> +	return vfs_xgetattr(path, stat);
>> +}
>> EXPORT_SYMBOL(vfs_getattr);
>> 
>> -int vfs_fstat(unsigned int fd, struct kstat *stat)
>> +/**
>> + * vfs_fstatx - Get the enhanced basic attributes by file descriptor
>> + * @fd: The file descriptor referring to the file of interest
>> + * @stat: The result structure to fill in.
>> + *
>> + * This function is a wrapper around vfs_xgetattr().  The main difference is
>> + * that it uses a file descriptor to determine the file location.
>> + *
>> + * The caller must have preset stat->query_flags and stat->request_mask as for
>> + * vfs_xgetattr().
>> + *
>> + * 0 will be returned on success, and a -ve error code if unsuccessful.
>> + */
>> +int vfs_fstatx(unsigned int fd, struct kstat *stat)
>> {
>> 	struct fd f = fdget_raw(fd);
>> 	int error = -EBADF;
>> 
>> 	if (f.file) {
>> -		error = vfs_getattr(&f.file->f_path, stat);
>> +		error = vfs_xgetattr(&f.file->f_path, stat);
>> 		fdput(f);
>> 	}
>> 	return error;
>> }
>> +EXPORT_SYMBOL(vfs_fstatx);
>> +
>> +/**
>> + * vfs_fstat - Get basic attributes by file descriptor
>> + * @fd: The file descriptor referring to the file of interest
>> + * @stat: The result structure to fill in.
>> + *
>> + * This function is a wrapper around vfs_getattr().  The main difference is
>> + * that it uses a file descriptor to determine the file location.
>> + *
>> + * 0 will be returned on success, and a -ve error code if unsuccessful.
>> + */
>> +int vfs_fstat(unsigned int fd, struct kstat *stat)
>> +{
>> +	stat->query_flags = 0;
>> +	stat->request_mask = STATX_BASIC_STATS;
>> +	return vfs_fstatx(fd, stat);
>> +}
>> EXPORT_SYMBOL(vfs_fstat);
>> 
>> -int vfs_fstatat(int dfd, const char __user *filename, struct kstat *stat,
>> -		int flag)
>> +/**
>> + * vfs_statx - Get basic and extra attributes by filename
>> + * @dfd: A file descriptor representing the base dir for a relative filename
>> + * @filename: The name of the file of interest
>> + * @flags: Flags to control the query
>> + * @stat: The result structure to fill in.
>> + *
>> + * This function is a wrapper around vfs_xgetattr().  The main difference is
>> + * that it uses a filename and base directory to determine the file location.
>> + * Additionally, the addition of AT_SYMLINK_NOFOLLOW to flags will prevent a
> 
> s/the addition of AT_SYMLINK_NOFOLLOW to/the use of AT_SYMLINK_NOFOLLOW in/
> 
> 
>> + * symlink at the given name from being referenced.
>> + *
>> + * The caller must have preset stat->request_mask as for vfs_xgetattr().  The
>> + * flags are also used to load up stat->query_flags.
>> + *
>> + * 0 will be returned on success, and a -ve error code if unsuccessful.
>> + */
>> +int vfs_statx(int dfd, const char __user *filename, int flags,
>> +	      struct kstat *stat)
>> {
>> 	struct path path;
>> 	int error = -EINVAL;
>> -	unsigned int lookup_flags = 0;
>> +	unsigned int lookup_flags = LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
>> 
>> -	if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT |
>> -		      AT_EMPTY_PATH)) != 0)
>> -		goto out;
>> +	if ((flags & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT |
>> +		       AT_EMPTY_PATH | KSTAT_QUERY_FLAGS)) != 0)
>> +		return -EINVAL;
>> 
>> -	if (!(flag & AT_SYMLINK_NOFOLLOW))
>> -		lookup_flags |= LOOKUP_FOLLOW;
>> -	if (flag & AT_EMPTY_PATH)
>> +	if (flags & AT_SYMLINK_NOFOLLOW)
>> +		lookup_flags &= ~LOOKUP_FOLLOW;
>> +	if (flags & AT_NO_AUTOMOUNT)
>> +		lookup_flags &= ~LOOKUP_AUTOMOUNT;
>> +	if (flags & AT_EMPTY_PATH)
>> 		lookup_flags |= LOOKUP_EMPTY;
>> +	stat->query_flags = flags;
>> +
>> retry:
>> 	error = user_path_at(dfd, filename, lookup_flags, &path);
>> 	if (error)
>> 		goto out;
>> 
>> -	error = vfs_getattr(&path, stat);
>> +	error = vfs_xgetattr(&path, stat);
>> 	path_put(&path);
>> 	if (retry_estale(error, lookup_flags)) {
>> 		lookup_flags |= LOOKUP_REVAL;
>> @@ -116,17 +227,65 @@ int vfs_fstatat(int dfd, const char __user *filename, struct kstat *stat,
>> out:
>> 	return error;
>> }
>> +EXPORT_SYMBOL(vfs_statx);
>> +
>> +/**
>> + * vfs_fstatat - Get basic attributes by filename
>> + * @dfd: A file descriptor representing the base dir for a relative filename
>> + * @filename: The name of the file of interest
>> + * @flags: Flags to control the query
>> + * @stat: The result structure to fill in.
>> + *
>> + * This function is a wrapper around vfs_statx().  The difference is that it
>> + * preselects basic stats only.  The flags are used to load up
>> + * stat->query_flags in addition to indicating symlink handling during path
>> + * resolution.
>> + *
>> + * 0 will be returned on success, and a -ve error code if unsuccessful.
>> + */
>> +int vfs_fstatat(int dfd, const char __user *filename, struct kstat *stat,
>> +		int flags)
>> +{
>> +	stat->request_mask = STATX_BASIC_STATS;
>> +	return vfs_statx(dfd, filename, flags, stat);
>> +}
>> EXPORT_SYMBOL(vfs_fstatat);
>> 
>> -int vfs_stat(const char __user *name, struct kstat *stat)
>> +/**
>> + * vfs_stat - Get basic attributes by filename
>> + * @filename: The name of the file of interest
>> + * @stat: The result structure to fill in.
>> + *
>> + * This function is a wrapper around vfs_statx().  The difference is that it
>> + * preselects basic stats only, terminal symlinks are followed regardless and a
> 
> s/terminal symlinks/symlinks in the basename/
> 
>> + * remote filesystem can't be forced to query the server.  If such is desired,
>> + * vfs_statx() should be used instead.
>> + *
>> + * 0 will be returned on success, and a -ve error code if unsuccessful.
>> + */
>> +int vfs_stat(const char __user *filename, struct kstat *stat)
>> {
>> -	return vfs_fstatat(AT_FDCWD, name, stat, 0);
>> +	stat->request_mask = STATX_BASIC_STATS;
>> +	return vfs_statx(AT_FDCWD, filename, 0, stat);
>> }
>> EXPORT_SYMBOL(vfs_stat);
>> 
>> +/**
>> + * vfs_lstat - Get basic attrs by filename, without following terminal symlink
>> + * @filename: The name of the file of interest
>> + * @stat: The result structure to fill in.
>> + *
>> + * This function is a wrapper around vfs_statx().  The difference is that it
>> + * preselects basic stats only, terminal symlinks are note followed regardless
> 
> s/terminal symlinks/symlinks in the basename/
> s/note/not/
> 
> 
>> + * and a remote filesystem can't be forced to query the server.  If such is
>> + * desired, vfs_statx() should be used instead.
>> + *
>> + * 0 will be returned on success, and a -ve error code if unsuccessful.
>> + */
>> int vfs_lstat(const char __user *name, struct kstat *stat)
>> {
>> -	return vfs_fstatat(AT_FDCWD, name, stat, AT_SYMLINK_NOFOLLOW);
>> +	stat->request_mask = STATX_BASIC_STATS;
>> +	return vfs_statx(AT_FDCWD, name, AT_SYMLINK_NOFOLLOW, stat);
>> }
>> EXPORT_SYMBOL(vfs_lstat);
>> 
>> @@ -141,7 +300,7 @@ static int cp_old_stat(struct kstat *stat, struct __old_kernel_stat __user * sta
>> {
>> 	static int warncount = 5;
>> 	struct __old_kernel_stat tmp;
>> -
>> +
>> 	if (warncount > 0) {
>> 		warncount--;
>> 		printk(KERN_WARNING "VFS: Warning: %s using old stat() call. Recompile your binary.\n",
>> @@ -166,7 +325,7 @@ static int cp_old_stat(struct kstat *stat, struct __old_kernel_stat __user * sta
>> #if BITS_PER_LONG == 32
>> 	if (stat->size > MAX_NON_LFS)
>> 		return -EOVERFLOW;
>> -#endif
>> +#endif
>> 	tmp.st_size = stat->size;
>> 	tmp.st_atime = stat->atime.tv_sec;
>> 	tmp.st_mtime = stat->mtime.tv_sec;
>> @@ -443,6 +602,82 @@ SYSCALL_DEFINE4(fstatat64, int, dfd, const char __user *, filename,
>> }
>> #endif /* __ARCH_WANT_STAT64 || __ARCH_WANT_COMPAT_STAT64 */
>> 
>> +/*
>> + * Set the statx results.
>> + */
>> +static long statx_set_result(struct kstat *stat, struct statx __user *buffer)
>> +{
>> +	uid_t uid = from_kuid_munged(current_user_ns(), stat->uid);
>> +	gid_t gid = from_kgid_munged(current_user_ns(), stat->gid);
>> +
>> +#define __put_timestamp(kts, uts) (				\
>> +		__put_user(kts.tv_sec,	uts.tv_sec	) ||	\
>> +		__put_user(kts.tv_nsec,	uts.tv_nsec	) ||		\
>> +		__put_user(0,		uts.__reserved	))
>> +
>> +	if (__put_user(stat->result_mask,	&buffer->stx_mask	) ||
>> +	    __put_user(stat->mode,		&buffer->stx_mode	) ||
>> +	    __clear_user(&buffer->__spare0, sizeof(buffer->__spare0))	  ||
>> +	    __put_user(stat->nlink,		&buffer->stx_nlink	) ||
>> +	    __put_user(uid,			&buffer->stx_uid	) ||
>> +	    __put_user(gid,			&buffer->stx_gid	) ||
>> +	    __put_user(stat->attributes,	&buffer->stx_attributes	) ||
>> +	    __put_user(stat->blksize,		&buffer->stx_blksize	) ||
>> +	    __put_user(MAJOR(stat->rdev),	&buffer->stx_rdev_major	) ||
>> +	    __put_user(MINOR(stat->rdev),	&buffer->stx_rdev_minor	) ||
>> +	    __put_user(MAJOR(stat->dev),	&buffer->stx_dev_major	) ||
>> +	    __put_user(MINOR(stat->dev),	&buffer->stx_dev_minor	) ||
>> +	    __put_timestamp(stat->atime,	&buffer->stx_atime	) ||
>> +	    __put_timestamp(stat->btime,	&buffer->stx_btime	) ||
>> +	    __put_timestamp(stat->ctime,	&buffer->stx_ctime	) ||
>> +	    __put_timestamp(stat->mtime,	&buffer->stx_mtime	) ||
>> +	    __put_user(stat->ino,		&buffer->stx_ino	) ||
>> +	    __put_user(stat->size,		&buffer->stx_size	) ||
>> +	    __put_user(stat->blocks,		&buffer->stx_blocks	) ||
>> +	    __clear_user(&buffer->__spare1, sizeof(buffer->__spare1))	  ||
>> +	    __clear_user(&buffer->__spare2, sizeof(buffer->__spare2)))
>> +		return -EFAULT;
>> +
>> +	return 0;
>> +}
>> +
>> +/**
>> + * sys_statx - System call to get enhanced stats
>> + * @dfd: Base directory to pathwalk from *or* fd to stat.
>> + * @filename: File to stat *or* NULL.
>> + * @flags: AT_* flags to control pathwalk.
>> + * @mask: Parts of statx struct actually required.
>> + * @buffer: Result buffer.
>> + *
>> + * Note that if filename is NULL, then it does the equivalent of fstat() using
>> + * dfd to indicate the file of interest.
>> + */
>> +SYSCALL_DEFINE5(statx,
>> +		int, dfd, const char __user *, filename, unsigned, flags,
>> +		unsigned int, mask,
>> +		struct statx __user *, buffer)
>> +{
>> +	struct kstat stat;
>> +	int error;
>> +
>> +	if ((flags & AT_STATX_SYNC_TYPE) == AT_STATX_SYNC_TYPE)
>> +		return -EINVAL;
>> +	if (!access_ok(VERIFY_WRITE, buffer, sizeof(*buffer)))
>> +		return -EFAULT;
>> +
>> +	memset(&stat, 0, sizeof(stat));
>> +	stat.query_flags = flags;
>> +	stat.request_mask = mask & STATX_ALL;
>> +
>> +	if (filename)
>> +		error = vfs_statx(dfd, filename, flags, &stat);
>> +	else
>> +		error = vfs_fstatx(dfd, &stat);
>> +	if (error)
>> +		return error;
>> +	return statx_set_result(&stat, buffer);
>> +}
>> +
>> /* Caller is here responsible for sufficient locking (ie. inode->i_lock) */
>> void __inode_add_bytes(struct inode *inode, loff_t bytes)
>> {
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 16d2b6e874d6..f153199566b4 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -2916,8 +2916,9 @@ extern const struct inode_operations page_symlink_inode_operations;
>> extern void kfree_link(void *);
>> extern int generic_readlink(struct dentry *, char __user *, int);
>> extern void generic_fillattr(struct inode *, struct kstat *);
>> -int vfs_getattr_nosec(struct path *path, struct kstat *stat);
>> +extern int vfs_xgetattr_nosec(struct path *path, struct kstat *stat);
>> extern int vfs_getattr(struct path *, struct kstat *);
>> +extern int vfs_xgetattr(struct path *, struct kstat *);
>> void __inode_add_bytes(struct inode *inode, loff_t bytes);
>> void inode_add_bytes(struct inode *inode, loff_t bytes);
>> void __inode_sub_bytes(struct inode *inode, loff_t bytes);
>> @@ -2935,6 +2936,8 @@ extern int vfs_lstat(const char __user *, struct kstat *);
>> extern int vfs_fstat(unsigned int, struct kstat *);
>> extern int vfs_fstatat(int , const char __user *, struct kstat *, int);
>> extern const char *vfs_get_link(struct dentry *, struct delayed_call *);
>> +extern int vfs_xstat(int, const char __user *, int, struct kstat *);
>> +extern int vfs_xfstat(unsigned int, struct kstat *);
>> 
>> extern int __generic_block_fiemap(struct inode *inode,
>> 				  struct fiemap_extent_info *fieinfo,
>> diff --git a/include/linux/stat.h b/include/linux/stat.h
>> index 075cb0c7eb2a..9b81dfcbb57a 100644
>> --- a/include/linux/stat.h
>> +++ b/include/linux/stat.h
>> @@ -19,19 +19,26 @@
>> #include <linux/uidgid.h>
>> 
>> struct kstat {
>> -	u64		ino;
>> -	dev_t		dev;
>> +	u32		query_flags;	/* Operational flags */
>> +#define KSTAT_QUERY_FLAGS (AT_STATX_SYNC_TYPE)
>> +	u32		request_mask;	/* What fields the user asked for */
>> +	u32		result_mask;	/* What fields the user got */
>> 	umode_t		mode;
>> 	unsigned int	nlink;
>> +	uint32_t	blksize;	/* Preferred I/O size */
>> +	u64		attributes;
>> +#define KSTAT_ATTR_FS_IOC_FLAGS		0x00000874 /* Attrs corresponding to FS_*_FL flags */
>> +	u64		ino;
>> +	dev_t		dev;
>> +	dev_t		rdev;
>> 	kuid_t		uid;
>> 	kgid_t		gid;
>> -	dev_t		rdev;
>> 	loff_t		size;
>> -	struct timespec  atime;
>> +	struct timespec	atime;
>> 	struct timespec	mtime;
>> 	struct timespec	ctime;
>> -	unsigned long	blksize;
>> -	unsigned long long	blocks;
>> +	struct timespec	btime;			/* File creation time */
>> +	u64		blocks;
>> };
>> 
>> #endif
>> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
>> index 91a740f6b884..980c3c9b06f8 100644
>> --- a/include/linux/syscalls.h
>> +++ b/include/linux/syscalls.h
>> @@ -48,6 +48,7 @@ struct stat;
>> struct stat64;
>> struct statfs;
>> struct statfs64;
>> +struct statx;
>> struct __sysctl_args;
>> struct sysinfo;
>> struct timespec;
>> @@ -902,5 +903,7 @@ asmlinkage long sys_pkey_mprotect(unsigned long start, size_t len,
>> 				  unsigned long prot, int pkey);
>> asmlinkage long sys_pkey_alloc(unsigned long flags, unsigned long init_val);
>> asmlinkage long sys_pkey_free(int pkey);
>> +asmlinkage long sys_statx(int dfd, const char __user *path, unsigned flags,
>> +			  unsigned mask, struct statx __user *buffer);
>> 
>> #endif
>> diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
>> index beed138bd359..813afd6eee71 100644
>> --- a/include/uapi/linux/fcntl.h
>> +++ b/include/uapi/linux/fcntl.h
>> @@ -63,5 +63,10 @@
>> #define AT_NO_AUTOMOUNT		0x800	/* Suppress terminal automount traversal */
>> #define AT_EMPTY_PATH		0x1000	/* Allow empty relative pathname */
>> 
>> +#define AT_STATX_SYNC_TYPE	0x6000	/* Type of synchronisation required from statx() */
>> +#define AT_STATX_SYNC_AS_STAT	0x0000	/* - Do whatever stat() does */
>> +#define AT_STATX_FORCE_SYNC	0x2000	/* - Force the attributes to be sync'd with the server */
>> +#define AT_STATX_DONT_SYNC	0x4000	/* - Don't sync attributes with the server */
>> +
>> 
>> #endif /* _UAPI_LINUX_FCNTL_H */
>> diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
>> index 7fec7e36d921..995e82fe019c 100644
>> --- a/include/uapi/linux/stat.h
>> +++ b/include/uapi/linux/stat.h
>> @@ -1,6 +1,7 @@
>> #ifndef _UAPI_LINUX_STAT_H
>> #define _UAPI_LINUX_STAT_H
>> 
>> +#include <linux/types.h>
>> 
>> #if defined(__KERNEL__) || !defined(__GLIBC__) || (__GLIBC__ < 2)
>> 
>> @@ -41,5 +42,124 @@
>> 
>> #endif
>> 
>> +/*
>> + * Timestamp structure for the timestamps in struct statx.
>> + */
>> +struct statx_timestamp {
>> +	__s64	tv_sec;		/* Number of seconds before or after midnight 1st Jan 1970 */
>> +	__s32	tv_nsec;	/* Number of nanoseconds before or after sec (0-999,999,999) */
> 
> Here, add a note in the comment: "Will be a negative value (if nonzero) if tv_sec is negative"
> 
> [...]
> 
> Cheers,
> 
> Michael
> 
> 
> 
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/
> --
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


Cheers, Andreas

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