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    Subject[PATCH 0/3] Extended file stat functions
    Date
    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_crtime;
    unsigned long long st_blocks;
    unsigned long long st_inode_version;
    unsigned long long st_data_version;
    unsigned long long query_flags;
    #define XSTAT_QUERY_CREATION_TIME 0x00000001ULL
    #define XSTAT_QUERY_INODE_VERSION 0x00000002ULL
    #define XSTAT_QUERY_DATA_VERSION 0x00000004ULL
    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
    version 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:

    [root@andromeda ~]# /tmp/xstat /afs/archive/linuxdev/fedora9/i386/repodata/
    xstat(/afs/archive/linuxdev/fedora9/i386/repodata/) = 152
    sv=0 qf=6 cr=0.0 iv=7a5 dv=5
    Size: 2048 Blocks: 0 IO Block: 4096 directory
    Device: 00:13 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/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/stat.c | 154 ++++++++++++++++++++++++++++---
    fs/utimes.c | 7 +
    include/linux/compat.h | 6 +
    include/linux/fs.h | 6 +
    include/linux/stat.h | 46 +++++++++
    include/linux/syscalls.h | 25 +++--
    include/linux/time.h | 2
    55 files changed, 353 insertions(+), 133 deletions(-)



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