linux-kernel - Re: hi-res mtime userspace interface

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Message-ID: <20080120085008.5c0e2b64@deepthought>
Date:	Sun, 20 Jan 2008 08:50:08 -0800
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Michael Clark <michael@...aparadigm.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: hi-res mtime userspace interface

On Sun, 20 Jan 2008 21:09:52 +0800
Michael Clark <michael@...aparadigm.com> wrote:

> Is there an existing linux userspace interface for accessing the 
> microsecond or nanosecond level (a|m|c)times of filesystems that support 
> them (e.g. ext4, xfs)? and possibly also the generation counters used by 
> NFS.
> 
> I notice sys_utimes is able to set microsecond (c|a|m)times but I can't 
> find an associated interface to read them (I've googled to no avail).
> 
> (also noticing freebsd and darwin's struct stat contains struct timespec 
> for these as well as an st_gen field - although I do realise how 
> incredibly difficult it would be to add these to linux's struct stat).
> 

Look at stat.

In /usr/include/bits/stat.h:
struct stat
  {
    __dev_t st_dev;		/* Device.  */
...
#ifdef __USE_MISC
    /* Nanosecond resolution timestamps are stored in a format
       equivalent to 'struct timespec'.  This is the type used
       whenever possible but the Unix namespace rules do not allow the
       identifier 'timespec' to appear in the <sys/stat.h> header.
       Therefore we have to handle the use of this header in strictly
       standard-compliant sources special.  */
    struct timespec st_atim;		/* Time of last access.  */
    struct timespec st_mtim;		/* Time of last modification.  */
    struct timespec st_ctim;		/* Time of last status change.  */
# define st_atime st_atim.tv_sec	/* Backward compatibility.  */
# define st_mtime st_mtim.tv_sec
# define st_ctime st_ctim.tv_sec
#else
    __time_t st_atime;			/* Time of last access.  */
    unsigned long int st_atimensec;	/* Nscecs of last access.  */
    __time_t st_mtime;			/* Time of last modification.  */
    unsigned long int st_mtimensec;	/* Nsecs of last modification.  */
    __time_t st_ctime;			/* Time of last status change.  */
    unsigned long int st_ctimensec;	/* Nsecs of last status change.  */
#endif
-- 
Stephen Hemminger <stephen.hemminger@...tta.com>
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