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

[Andreas Dilger]

On Nov 20, 2015, at 9:50 AM, Casey Schaufler <casey@xxxxxxxxxxxxxxxx> 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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