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Gmane
From: David Howells <dhowells <at> redhat.com>
Subject: [PATCH 0/3] Extended file stat functions [ver #2]
Newsgroups: gmane.linux.kernel
Date: Wednesday 30th June 2010 01:16:56 UTC (over 6 years ago)
Implement a pair of new system calls to provide extended and further
extensible
stat functions.

The third of the associated patches provides these new system calls:

	struct xstat_dev {
		unsigned int	major;
		unsigned int	minor;
	};

	struct xstat_time {
		unsigned long long	tv_sec;
		unsigned long long	tv_nsec;
	};

	struct xstat {
		unsigned int		struct_version;
	#define XSTAT_STRUCT_VERSION	0
		unsigned int		st_mode;
		unsigned int		st_nlink;
		unsigned int		st_uid;
		unsigned int		st_gid;
		unsigned int		st_blksize;
		struct xstat_dev	st_rdev;
		struct xstat_dev	st_dev;
		unsigned long long	st_ino;
		unsigned long long	st_size;
		struct xstat_time	st_atime;
		struct xstat_time	st_mtime;
		struct xstat_time	st_ctime;
		struct xstat_time	st_btime;
		unsigned long long	st_blocks;
		unsigned long long	st_gen;
		unsigned long long	st_data_version;
		unsigned long long	query_flags;
	#define XSTAT_QUERY_SIZE		0x00000001ULL
	#define XSTAT_QUERY_NLINK		0x00000002ULL
	#define XSTAT_QUERY_AMC_TIMES		0x00000004ULL
	#define XSTAT_QUERY_CREATION_TIME	0x00000008ULL
	#define XSTAT_QUERY_BLOCKS		0x00000010ULL
	#define XSTAT_QUERY_INODE_GENERATION	0x00000020ULL
	#define XSTAT_QUERY_DATA_VERSION	0x00000040ULL
	#define XSTAT_QUERY__ORDINARY_SET	0x00000017ULL
	#define XSTAT_QUERY__GET_ANYWAY		0x0000007fULL
	#define XSTAT_QUERY__DEFINED_SET	0x0000007fULL
		unsigned long long	extra_results[0];
	};

	ssize_t ret = xstat(int dfd,
			    const char *filename,
			    unsigned atflag,
			    struct xstat *buffer,
			    size_t buflen);

	ssize_t ret = fxstat(int fd,
			     struct xstat *buffer,
			     size_t buflen);

which are more fully documented in that patch's description.

The bonuses of these new stat functions are:

 (1) The fields in the xstat struct are cleaned up.  There are no split or
     duplicated fields.

 (2) Some extra information is made available (file creation time, inode
     generation number and data version number) where provided by the
     underlying filesystem.

     These are implemented here for Ext4 and AFS, but could also be
provided
     for CIFS, NTFS and BtrFS and probably others.

 (3) The structure is versioned and extensible, meaning that further new
system
     calls shouldn't be required.

Note that no lstat() equivalent is required as that can be implemented
through
xstat() with atflag == 0.


The first patch makes const a bunch of system call userspace string/buffer
arguments.  I can then make sys_xstat()'s filename pointer const too
(though
the entire first patch is not required for that).

The second patch makes the AFS filesystem use i_generation for the vnode ID
uniquifier rather than i_version, and assigns i_version to hold the AFS
data
version number, making them more logical for when I want to get at them
from
afs_getattr().


There's a test program attached to the description for patch 3.  It can be
run
as follows:

	[[email protected] ~]# /tmp/xstat
/afs/archive/linuxdev/fedora9/i386/repodata/
	xstat(/afs/archive/linuxdev/fedora9/i386/repodata/) = 152
	sv=0 qf=77 cr=0.0 iv=7a5 dv=5
	  Size: 2048            Blocks: 0          IO Block: 4096    directory
	Device: 00:15           Inode: 83          Links: 2
	Access: (0755/drwxr-xr-x)  Uid: 75338   Gid: 0
	Access: 2008-11-05 20:00:12.000000000+0000
	Modify: 2008-11-05 20:00:12.000000000+0000
	Change: 2008-11-05 20:00:12.000000000+0000
	Inode version: 7a5h
	Data version: 5h


Things that need consideration:

 (1) Is it worth retaining the ability to arbitrarily add extra bits onto
the
     end of the stat buffer?  And what's the best way to do this?

     I've defined a way that from userspace involves assigning bits in
     query_flags to extra results that you might want.  But this could
instead
     be done, say, by just upping the struct version number any time we
want to
     pass back more information.  Alternatively, we could go for a tagged
data
     method, perhaps using the same format as the recvmsg() control message
     field.

     If we use tagged data then rather than being selective, we could just
     return as many tagged data items as we feel the user might want and we
can
     cram into the buffer.  That could be rather slow, though.

 (2) What extra bits of information might we like to see available through
the
     stat interface?  Security labels?  NFS file IDs?  Xattrs?

     If we went for a tagged data method, xstat() could be modified to take
a
     list of tags as an argument, and could then return arbitrarily-sized
     tagged results, including fs-specific stuff.

 (3) Does st_blksize really need to be 64 bits on a 64-bit system?  Or can
it
     be 32-bits?  Are we really likely to see something with a 4Gb+
blocksize?

 (4) Should the inode number and data version number fields be 128-bit?

David
---

David Howells (3):
      Add a pair of system calls to make extended file stats available
      AFS: Use i_generation not i_version for the vnode uniquifier
      Mark arguments to certain syscalls as being const


 arch/alpha/kernel/osf_sys.c             |    6 +
 arch/alpha/kernel/process.c             |    2 
 arch/arm/kernel/sys_arm.c               |    4 -
 arch/arm/kernel/sys_oabi-compat.c       |    6 +
 arch/avr32/include/asm/syscalls.h       |    2 
 arch/avr32/kernel/process.c             |    3 -
 arch/blackfin/kernel/process.c          |    2 
 arch/frv/kernel/process.c               |    3 -
 arch/h8300/kernel/process.c             |    2 
 arch/ia64/include/asm/unistd.h          |    2 
 arch/ia64/kernel/process.c              |    2 
 arch/m32r/kernel/process.c              |    3 -
 arch/m68k/kernel/process.c              |    2 
 arch/m68knommu/kernel/process.c         |    2 
 arch/microblaze/kernel/sys_microblaze.c |    2 
 arch/mips/kernel/syscall.c              |    2 
 arch/mn10300/kernel/process.c           |    2 
 arch/parisc/hpux/fs.c                   |    7 +
 arch/powerpc/kernel/process.c           |    2 
 arch/powerpc/kernel/sys_ppc32.c         |    2 
 arch/s390/kernel/compat_linux.c         |   10 +-
 arch/s390/kernel/compat_linux.h         |   10 +-
 arch/s390/kernel/entry.h                |    2 
 arch/s390/kernel/process.c              |    2 
 arch/sh/include/asm/syscalls_32.h       |    2 
 arch/sh/include/asm/syscalls_64.h       |    2 
 arch/sh/kernel/process_64.c             |    2 
 arch/sparc/kernel/sys_sparc32.c         |    7 +
 arch/um/kernel/exec.c                   |    6 +
 arch/um/kernel/internal.h               |    2 
 arch/um/kernel/syscall.c                |    2 
 arch/x86/ia32/sys_ia32.c                |   14 +-
 arch/x86/include/asm/sys_ia32.h         |   12 +-
 arch/x86/include/asm/syscalls.h         |    2 
 arch/x86/include/asm/unistd_32.h        |    4 +
 arch/x86/include/asm/unistd_64.h        |    4 +
 arch/x86/kernel/entry_64.S              |    4 -
 arch/x86/kernel/process.c               |    2 
 arch/xtensa/kernel/process.c            |    2 
 fs/afs/dir.c                            |    8 +
 fs/afs/fsclient.c                       |    3 -
 fs/afs/inode.c                          |   22 ++--
 fs/compat.c                             |   23 ++--
 fs/ecryptfs/inode.c                     |    1 
 fs/ext4/ext4.h                          |    2 
 fs/ext4/file.c                          |    2 
 fs/ext4/inode.c                         |   27 ++++-
 fs/ext4/namei.c                         |    2 
 fs/ext4/symlink.c                       |    2 
 fs/nfs/inode.c                          |   38 +++++--
 fs/nfsd/nfs3proc.c                      |    1 
 fs/nfsd/nfs3xdr.c                       |    2 
 fs/nfsd/nfs4xdr.c                       |    2 
 fs/nfsd/nfsproc.c                       |    3 +
 fs/nfsd/nfsxdr.c                        |    1 
 fs/stat.c                               |  178
++++++++++++++++++++++++++++---
 fs/utimes.c                             |    7 +
 include/linux/compat.h                  |    6 +
 include/linux/fs.h                      |    8 +
 include/linux/stat.h                    |   88 +++++++++++++++
 include/linux/syscalls.h                |   25 +++-
 include/linux/time.h                    |    2 
 62 files changed, 456 insertions(+), 146 deletions(-)

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