Re: [PATCH 6/6] [RFC] ext4: super: extend timestamps to 40 bits

On Thu, Jun 21, 2018 at 7:46 PM, Andreas Dilger [off-list ref] wrote:

quoted

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 0c4c2201b3aa..2063d4e5ed08 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c

@@ -312,6 +312,20 @@ void ext4_itable_unused_set(struct super_block *sb,
              bg->bg_itable_unused_hi = cpu_to_le16(count >> 16);

}

+static void ext4_update_tstamp(__le32 *lo, __u8 *hi)

Would it be better to wrap this in a macro, something like:

#define ext4_update_tstamp(es, tstamp) \
        __ext4_update_tstamp(&(es)->tstamp, &(es)->tstamp ## _hi)
#define ext4_get_tstamp(es, tstamp) \
        __ext4_get_tstamp(&(es)->tstamp, &(es)->tstamp ## _hi)

So that it can be used in the callers more easily:

        ext4_update_tstamp(es, s_last_error_time);
        time = ext4_get_tstamp(es, s_last_error_time);

I generally try to avoid concatenating identifiers like this, as it makes
it much harder to grep for where a particular symbol or
struct member gets used.

quoted

+{
+     time64_t now = ktime_get_real_seconds();
+
+     now = clamp_val(now, 0, 0xffffffffffull);

Long strings of "0xfff..." are hard to get correct.  This looks right,
but it may be easier to be sure it is correct with something like:

        /* timestamps have a 32-bit low field and 8-bit high field */
        now = clamp_val(now, 0, (1ULL << 40) - 1);

Yes, good idea. I'm surprised we don't have a generic macro for that yet
(or maybe I just couldn't find it)

quoted

@@ -249,6 +251,12 @@ static void *calc_ptr(struct ext4_attr *a, struct ext4_sb_info *sbi)
      return NULL;

}

+static ssize_t print_time(char *buf, __le32 lo, __u8 hi)

It would probably be more consistent to name this "print_tstamp()"
since it isn't strictly a "time" as one would expect.

Ok.

quoted

+{
+     return snprintf(buf, PAGE_SIZE, "%lld",
+                     ((time64_t)hi << 32) + le32_to_cpu(lo));
+}

Similarly, wrap this with:

#define print_tstamp(buf, es, tstamp) \
        __print_tstamp(buf, &(es)->tstamp, &(es)->tstamp ## _hi)

Ok. I'll integrate all of the above and post as a non-RFC patch then
after some testing.

      Arnd