On Tue, Jun 29, 2010 at 3:02 PM, David Howells <dhowells@xxxxxxxxxx> wrote:
> 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.
NFSv4 protocol also has a "recommended attribute" for create time that servers
should return if possible (which presumably now it would be possible to return
for Linux servers)
time_create 50 nfstime4 R/W The time of
creation of the object.
SMB2 protocol also returns the equivalent.
> (3) The structure is versioned and extensible, meaning that further new system
> calls shouldn't be required.
How does a fs return an "unknown" value for one
(e.g. version field) ... 0 or -1 or ...
> (2) What extra bits of information might we like to see available through the
> stat interface? Security labels? NFS file IDs? Xattrs?
The list of mandatory ones for NFS is fairly small, the list of recommended
one for NFSv4 is larger (see page 44ff of
http://www.ietf.org/rfc/rfc3530.txt e.g.)
One hole that this reminded me about is how to return the superblock
time granularity (for NFSv4 this is attribute 51 "time_delta" which
is called on a superblock not on a file). We run into time rounding
issues with Samba too.
>
> (4) Should the inode number and data version number fields be 128-bit?
This is tricky for SMB2, if you can also provide a device id (or an object id of
some sort for the superblock) then 64 bit inode number is ok.
--
Thanks,
Steve
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