Re: [PATCH v8 08/20] adfs: Fill in max and min timestamps in sb

[Deepa Dinamani]

On Tue, Aug 20, 2019 at 9:28 AM Matthew Wilcox  wrote:
>
> On Sun, Aug 18, 2019 at 09:58:05AM -0700, Deepa Dinamani wrote:
> > Note that the min timestamp is assumed to be
> > 01 Jan 1970 00:00:00 (Unix epoch). This is consistent
> > with the way we convert timestamps in adfs_adfs2unix_time().
>
> That's not actually correct.  RISC OS timestamps are centiseconds since
> 1900 stored in 5 bytes.

The timestamp can hold earlier values but the fs implementation
explicitly rejects those in adfs_adfs2unix_time() too_early check.
We could fix the implementation to not throw away times before 1970.
Are you suggesting we want to do this?
I could post a separate patch to fix this or we could do it as part of
the series.

 static void
 adfs_adfs2unix_time(struct timespec64 *tv, struct inode *inode)
 {
 unsigned int high, low;
 static const s64 nsec_unix_epoch_diff_risc_os_epoch =
RISC_OS_EPOCH_DELTA * NSEC_PER_SEC;
 s64 nsec;

 if (!adfs_inode_is_stamped(inode))
 goto cur_time;

 high = ADFS_I(inode)->loadaddr & 0xFF; /* top 8 bits of timestamp */
 low  = ADFS_I(inode)->execaddr;/* bottom 32 bits of timestamp */

 /* convert 40-bit centi-seconds to 32-bit seconds
  * going via nanoseconds to retain precision
  */
 nsec = (((s64) high << 32) | (s64) low) * 1000; /* cs to ns */

 /* Files dated pre  01 Jan 1970 00:00:00. */
 if (nsec < nsec_unix_epoch_diff_risc_os_epoch)
 goto too_early;

 /* convert from RISC OS to Unix epoch */
 nsec -= nsec_unix_epoch_diff_risc_os_epoch;

 *tv = ns_to_timespec64(nsec);
 return;

  cur_time:
 *tv = current_time(inode);
 return;

  too_early:
 tv->tv_sec = tv->tv_nsec = 0;
 return;
 }

-Deepa

Re: [PATCH v8 08/20] adfs: Fill in max and min timestamps in sb

[Matthew Wilcox]

On Sun, Aug 18, 2019 at 09:58:05AM -0700, Deepa Dinamani wrote:
> Note that the min timestamp is assumed to be
> 01 Jan 1970 00:00:00 (Unix epoch). This is consistent
> with the way we convert timestamps in adfs_adfs2unix_time().

That's not actually correct.  RISC OS timestamps are centiseconds since
1900 stored in 5 bytes.

> Signed-off-by: Deepa Dinamani 
> ---
>  fs/adfs/adfs.h  | 13 +
>  fs/adfs/inode.c |  8 ++--
>  fs/adfs/super.c |  2 ++
>  3 files changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/adfs/adfs.h b/fs/adfs/adfs.h
> index b7e844d2f321..dca8b23aa43f 100644
> --- a/fs/adfs/adfs.h
> +++ b/fs/adfs/adfs.h
> @@ -3,6 +3,19 @@
>  #include 
>  #include 
>  
> +/*
> + * 01 Jan 1970 00:00:00 (Unix epoch) as seconds since
> + * 01 Jan 1900 00:00:00 (RISC OS epoch)
> + */
> +#define RISC_OS_EPOCH_DELTA 2208988800LL
> +
> +/*
> + * Convert 40 bit centi seconds to seconds
> + * since 01 Jan 1900 00:00:00 (RISC OS epoch)
> + * The result is 2248-06-03 06:57:57 GMT
> + */
> +#define ADFS_MAX_TIMESTAMP ((0xFFLL / 100) - RISC_OS_EPOCH_DELTA)
> +
>  /* Internal data structures for ADFS */
>  
>  #define ADFS_FREE_FRAG0
> diff --git a/fs/adfs/inode.c b/fs/adfs/inode.c
> index 124de75413a5..41eca1c451dc 100644
> --- a/fs/adfs/inode.c
> +++ b/fs/adfs/inode.c
> @@ -167,11 +167,7 @@ static void
>  adfs_adfs2unix_time(struct timespec64 *tv, struct inode *inode)
>  {
>   unsigned int high, low;
> - /* 01 Jan 1970 00:00:00 (Unix epoch) as nanoseconds since
> -  * 01 Jan 1900 00:00:00 (RISC OS epoch)
> -  */
> - static const s64 nsec_unix_epoch_diff_risc_os_epoch =
> - 22089888000LL;
> + static const s64 nsec_unix_epoch_diff_risc_os_epoch = 
> RISC_OS_EPOCH_DELTA * NSEC_PER_SEC;
>   s64 nsec;
>  
>   if (!adfs_inode_is_stamped(inode))
> @@ -216,7 +212,7 @@ adfs_unix2adfs_time(struct inode *inode, unsigned int 
> secs)
>   if (adfs_inode_is_stamped(inode)) {
>   /* convert 32-bit seconds to 40-bit centi-seconds */
>   low  = (secs & 255) * 100;
> - high = (secs / 256) * 100 + (low >> 8) + 0x336e996a;
> + high = (secs / 256) * 100 + (low >> 8) + 
> (RISC_OS_EPOCH_DELTA*100/256);
>  
>   ADFS_I(inode)->loadaddr = (high >> 24) |
>   (ADFS_I(inode)->loadaddr & ~0xff);
> diff --git a/fs/adfs/super.c b/fs/adfs/super.c
> index 65b04ebb51c3..f074fe7d7158 100644
> --- a/fs/adfs/super.c
> +++ b/fs/adfs/super.c
> @@ -463,6 +463,8 @@ static int adfs_fill_super(struct super_block *sb, void 
> *data, int silent)
>   asb->s_map_size = dr->nzones | (dr->nzones_high << 8);
>   asb->s_map2blk  = dr->log2bpmb - dr->log2secsize;
>   asb->s_log2sharesize= dr->log2sharesize;
> + sb->s_time_min  = 0;
> + sb->s_time_max  = ADFS_MAX_TIMESTAMP;
>  
>   asb->s_map = adfs_read_map(sb, dr);
>   if (IS_ERR(asb->s_map)) {
> -- 
> 2.17.1
>