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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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