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    SubjectRe: [RFC][PATCH 00/12] Enhanced file stat system call
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    On Nov 20, 2015, at 9:50 AM, Casey Schaufler <casey@schaufler-ca.com> wrote:
    > On 11/20/2015 6:54 AM, David Howells wrote:
    >> Implement new system calls to provide enhanced file stats and enhanced
    >> filesystem stats. The patches can be found here:
    >>
    >> http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=xstat
    >>
    >>
    >> ===========
    >> DESCRIPTION
    >> ===========
    >>
    >> 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.
    >
    > How about relevant xattrs? SELinux context, ACL, that sort of thing.
    > The fact that these are optional should be taken care of by (4).

    Given that there are a wide variety of xattrs that different apps might be
    interested in, this would probably be better served by an enhancement to
    getxattr() or listxattr() to be able to retrieve a whole list of xattrs
    at once, possibly with some wildcard support (e.g. "security.*") instead
    of returning all or a specific subset of xattrs with statx() (which is
    geared toward fixed-size attributes).

    Cheers, Andreas


    >> 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().
    >>
    >>
    >> =======
    >> TESTING
    >> =======
    >>
    >> Test programs are added into samples/statx/ by the appropriate patches.
    >>
    >> David
    >> ---
    >> 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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    >
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    Cheers, Andreas





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