On Tue, Nov 12, 2013 at 06:41:27PM +0000, David Howells wrote: > > Implement a new system call to provide an extended and further extensible stat > function. > > ======= > CHANGES > ======= > > (*) Added an optional auxiliary data buffer pointer argument to sys_statxat() > and moved some of the stuff into it. > > (*) Discarded "has an ACL info flag" for now. > > (*) AFS doesn't need to set time granularity itself as the default is 1s > anyway. > > > =========== > DESCRIPTION > =========== > > The second of the associated patches is the main patch that provides this new > system call: > > long ret = statxat(int dfd, > const char *filename, > unsigned atflag, > unsigned mask, > struct statx *buffer, > struct statx_auxinfo *auxinfo); > > which is more fully documented in the main patch's description. > > This new stat function 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: Ask for just those details of interest, and allow a > netfs (such as NFS) to approximate anything not of interest, possibly > without going to the server. > > (3) Heavyweight stat: Force a netfs to go to the server, even if it thinks its > cached attributes are up to date. I'm not following the lightweight/heavyweight thing: so this is encoded in the mask? So it's just a 1-bit value per attribute? Because it seems like there are potentially 3 different behaviors: - definitely get this from the server now even if you normally wouldn't. - definitely don't go to the server even if you know your cache is stale. - do whatever you'd normally do (check how old your cache is or whatever). I guess this is what you're asking in "considerations" below. --b. > (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 appending further data > after the end of the standard return data. > > Note that no lstat() equivalent is required as that can be implemented through > statxat() with atflag == 0. There is also no fstat() equivalent as that can be > implemented through statxat() with filename == NULL and the relevant fd passed > as dfd. > > > ======= > PATCHES > ======= > > Patch 1 introduces IOC flags for Windows Hidden, Archive and System attributes. > > Patch 2 defines the statxat() system call. > > Patch 3 implements extended stat facilities for AFS. Other fs patches to go > through their respective trees once the core is in. > > > ============== > CONSIDERATIONS > ============== > > Should the default for a network fs be to do an unconditional (heavyweight) > stat with a flag to suppress going to the server to update the locally held > attributes and flushing pending writebacks? > > Is it useful to pass the volume ID out? Or should statfs() be used for this? > > Is there anything else I can usefully add at the moment? > > > ========== > TO BE DONE > ========== > > Autofs, ntfs, btrfs, ... > > I should perhaps use u8/u32/u64 rather than uint8/32/64_t. > > Handle remote filesystems being offline and indicate this with > STATX_INFO_OFFLINE. > > Should a "light stat" be explicitly requested by its own AT_ flag? > > > ======= > TESTING > ======= > > There's a test program attached to the description for the main patch. It can > be run as follows: > [root@andromeda tmp]# ./xstat -R /mnt/foo > > xstat(/mnt/foo) = 0 > 0000: 000081a40000ffef 0000000000000001 0000020000000000 0000100000080000 > 0020: 0000000000000000 0000000600000008 000000004f88499a 0000000136fd9208 > 0040: 000000004f88499a 0000000136fd9208 000000004f8849b9 0000000106daf187 > 0060: 000000004f8849b9 0000000106daf187 000000000000000c 000000000000000f > 0080: 0000000000000008 00000000484ebbef 0000000000000025 5949ebd4711efd82 > 00a0: d3250b5c15d5e380 0000000000000000 0000000000000000 0000000000000000 > 00c0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > 00e0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > results=ffef > Size: 15 Blocks: 8 IO Block: 4096 regular file > Device: 08:06 Inode: 12 Links: 1 > Access: (0644/-rw-r--r--) Uid: 0 > Gid: 0 > Access: 2012-04-13 16:43:22.922587656+0100 > Modify: 2012-04-13 16:43:53.115011975+0100 > Change: 2012-04-13 16:43:53.115011975+0100 > Create: 2012-04-13 16:43:22.922587656+0100 > Inode version: 484ebbefh > Data version: 25h > Inode flags: 00080000 (-------- ----e--- -------- --------) > Information: 00000200 (-------- -------- ------a- --------) > Volume ID: 82fd1e71d4eb4959-80e3d5155c0b25d3 > > David > --- > David Howells (3): > statxat: Provide IOC flags for Windows fs attributes > statxat: Add a system call to make extended file stats available > statxat: AFS: Return enhanced basic attributes > > > arch/x86/ia32/sys_ia32.c | 2 > arch/x86/syscalls/syscall_32.tbl | 1 > arch/x86/syscalls/syscall_64.tbl | 1 > fs/afs/inode.c | 46 ++++- > fs/ceph/inode.c | 2 > fs/cifs/inode.c | 5 - > fs/compat.c | 2 > fs/nfsd/nfsxdr.c | 2 > fs/stat.c | 348 ++++++++++++++++++++++++++++++++++++-- > include/linux/fs.h | 3 > include/linux/stat.h | 16 ++ > include/linux/syscalls.h | 6 + > include/uapi/linux/fcntl.h | 1 > include/uapi/linux/fs.h | 7 + > include/uapi/linux/stat.h | 164 ++++++++++++++++++ > 15 files changed, 567 insertions(+), 39 deletions(-) > > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
