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    SubjectRe: [RFC][PATCH 00/12] Enhanced file stat system call
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    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).

    >
    > 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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