[RFC][PATCH 00/12] Enhanced file stat system call

David Howells dhowells at redhat.com
Fri Nov 20 14:54:22 UTC 2015

Implement new system calls to provide enhanced file stats and enhanced
filesystem stats.  The patches can be found here:



The third patch provides this new system call:

	long ret = statx(int dfd,
			 const char *filename,
			 unsigned atflag,
			 unsigned mask,
			 struct statx *buffer);

This is an enhanced file stat function that provides a number of useful
features, in summary:

 (1) More information: creation time, data version number,
     flags/attributes.  A subset of these is available through a number of
     filesystems (such as CIFS, NFS, AFS, Ext4 and BTRFS).

 (2) Lightweight stat (AT_NO_ATTR_SYNC): Ask for just those details of
     interest, and allow a network fs to approximate anything not of
     interest, without going to the server.

 (3) Heavyweight stat (AT_FORCE_ATTR_SYNC): Force a network fs to flush
     buffers and go to the server, even if it thinks its cached attributes
     are up to date.

 (4) 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.

 (5) Make the fields a consistent size on all arches, and make them large.

 (6) Can be extended by using more request flags and using up the padding
     space in the statx struct.

Note that no lstat() equivalent is required as that can be implemented
through statx() with atflag == 0.  There is also no fstat() equivalent as
that can be implemented through statx() with filename == NULL and the
relevant fd passed as dfd.

The seventh patch provides another new system call:

	long ret = fsinfo(int dfd,
			  const char *filename,
			  unsigned atflag,
			  unsigned request,
			  void *buffer);

This is an enhanced filesystem stat and information retrieval function that
provides more information, in summary:

 (1) All the information provided by statfs() and more.  The fields are
     made large.

 (2) Provides information about timestamp range and resolution to
     complement statx().

 (3) Provides information about IOC flags supported in statx()'s return.

 (4) Provides volume binary IDs and UUIDs.

 (5) Provides the filesystem name according to the kernel as a string
     (eg. "ext4" or "nfs3") in addition to the magic number.

 (6) Provides information obtained from network filesystems, such as volume
     and domain names.

 (7) Has lots of spare space that can be used for future extenstions and a
     bit mask indicating what was provided.

Note that I've added a 'request' identifier.  This is to select the set of
data to be returned.  The idea is that 'buffer' points to a fixed-size
struct selected by request.  Currently only 0 is available and this refers
to 'struct fsinfo'.  However, I could split up the buffer into say 3:

 (0) statfs-type information

 (1) Timestamp and IOC flags info.

 (2) Network fs strings.

However, some of this might be better retrieved through getxattr().


Test programs are added into samples/statx/ by the appropriate patches.

David Howells (12):
      Ext4: Fix extended timestamp encoding and decoding
      statx: Provide IOC flags for Windows fs attributes
      statx: Add a system call to make enhanced file info available
      statx: AFS: Return enhanced file attributes
      statx: Ext4: Return enhanced file attributes
      statx: NFS: Return enhanced file attributes
      statx: CIFS: Return enhanced attributes
      fsinfo: Add a system call to make enhanced filesystem info available
      fsinfo: Ext4: Return information through the filesystem info syscall
      fsinfo: AFS: Return information through the filesystem info syscall
      fsinfo: NFS: Return information through the filesystem info syscall
      fsinfo: CIFS: Return information through the filesystem info syscall

 arch/x86/entry/syscalls/syscall_32.tbl |    2 
 arch/x86/entry/syscalls/syscall_64.tbl |    2 
 fs/afs/inode.c                         |   23 ++
 fs/afs/super.c                         |   39 ++++
 fs/cifs/cifsfs.c                       |   25 +++
 fs/cifs/cifsfs.h                       |    4 
 fs/cifs/cifsglob.h                     |    8 +
 fs/cifs/dir.c                          |    2 
 fs/cifs/inode.c                        |  124 ++++++++++---
 fs/cifs/netmisc.c                      |    4 
 fs/exportfs/expfs.c                    |    4 
 fs/ext4/ext4.h                         |   24 ++-
 fs/ext4/file.c                         |    2 
 fs/ext4/inode.c                        |   31 +++
 fs/ext4/namei.c                        |    2 
 fs/ext4/super.c                        |   39 ++++
 fs/ext4/symlink.c                      |    2 
 fs/nfs/inode.c                         |   45 ++++-
 fs/nfs/internal.h                      |    1 
 fs/nfs/nfs4super.c                     |    1 
 fs/nfs/super.c                         |   58 ++++++
 fs/ntfs/time.h                         |    2 
 fs/stat.c                              |  305 +++++++++++++++++++++++++++++---
 fs/statfs.c                            |  218 +++++++++++++++++++++++
 include/linux/fs.h                     |    7 +
 include/linux/stat.h                   |   14 +
 include/linux/syscalls.h               |    6 +
 include/linux/time64.h                 |    2 
 include/uapi/linux/fcntl.h             |    2 
 include/uapi/linux/fs.h                |    7 +
 include/uapi/linux/stat.h              |  185 +++++++++++++++++++
 samples/Makefile                       |    3 
 samples/statx/Makefile                 |   13 +
 samples/statx/test-fsinfo.c            |  179 +++++++++++++++++++
 samples/statx/test-statx.c             |  273 +++++++++++++++++++++++++++++
 35 files changed, 1558 insertions(+), 100 deletions(-)
 create mode 100644 samples/statx/Makefile
 create mode 100644 samples/statx/test-fsinfo.c
 create mode 100644 samples/statx/test-statx.c

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