Mark Harris <mhlk@xxxxxx> wrote:
> > struct xstat_time {
> > unsigned long long tv_sec, tv_nsec;
> > };
>
> unsigned? Existing filesystems support on-disk timestamps
> representing times prior to the epoch.
I suppose it doesn't hurt to make is signed. It's large enough...
Looking at it again, having a 64-bit field for tv_nsec is overkill. It can't
(or shouldn't) exceed 999,999,999 - well within the capability of a 32-bit
unsigned integer.
So how about using up the dead space for what Steve French wanted:
| 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.
By doing something like:
struct xstat_time {
signed long long tv_sec;
unsigned int tv_nsec;
unsigned short tv_granularity;
unsigned short tv_gran_units;
};
Where tv_granularity is the minimum granularity for tv_sec and tv_nsec given
as a quantity of tv_gran_units. tv_gran_units could then be a constant, such
as:
XSTAT_NANOSECONDS_GRANULARITY
XSTAT_MICROSECONDS_GRANULARITY
XSTAT_MILLISECONDS_GRANULARITY
XSTAT_SECONDS_GRANULARITY
XSTAT_MINUTES_GRANULARITY
XSTAT_HOURS_GRANULARITY
XSTAT_DAYS_GRANULARITY
So, for example, FAT times are a 2s granularity, so FAT would set
tv_granularity to 2 and tv_gran_units to XSTAT_SECONDS_GRANULARITY.
We could even support picosecond granularity if we made tv_nsec a 5-byte
field (tv_psec):
struct xstat_time {
signed long long tv_sec;
unsigned long long tv_gran_units : 8;
unsigned long long tv_granularity : 16;
unsigned long long tv_psec : 48;
};
but that's probably excessive. Does any filesystem we currently support need
that?
David
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