Re: [PATCH] PUFFS with cache TTL from filesystem

[yamt%mwd.biglobe.ne.jp@localhost (YAMAMOTO Takashi)]

hi,

> YAMAMOTO Takashi <yamt%mwd.biglobe.ne.jp@localhost> wrote:
> 
>> - i feel that the api is too specific to the use of libperfuse.
>>       - it should not require puffs_node.
> 
> I started without puffs_node at once but that require changing vnop
> methods prototypes and makes them heavyweight. The chosen solution has
> merits for the sake of readability and backward compatibility.

if you want to avoid prototype changes, another set of puffs_newinfo_setfoo()
would be enough for DIROPs.

GETATTR needs another versions of op callbacks, yes.  it doesn't seem
like a big problem to me, tho.

> 
> 
>>       - i think you mixed up at least two separate features.
>>         they ought to have separate flags.
>>               - DIROP's ability to return file attribute
>>               - attribute TTLs
>> - it would be better to allow file server choose if it returns attributes
>>   on DIROPs per-request basis rather than per-mount.  like nfsv3.
> 
> Those two are the same problem. 
> 
> We could simply ignore attributes when attribute TTL is set to 0. It
> makes sense since on lookup/create/mkdir/mknod/symlink, the attributes
> returned by the fileystem have no immediate use by the kernel. A TTL set
> to 0 means they should not be used for a subsequent getattr, so we can
> cut corners and just not save them.
> 
> And if the filesystem wants to set attributes without a TTL, there is
> always the solution to set a far away TTL. Perahps I could just define a
> magic value for that.

it sounds fine to me.  thanks for explanation.

> 
>> - as new functions returns a pointer, it's better to follow
>>   the existing naming convention.  ie. "p" of puffs_pn_getvap
> 
> Right.
> 
>> - please handle ticks wraparounds.
> 
> Any example of some code where this is done?

common ways are
        - use a less-wraparound-prune clock like time_uptime unless you
          really need tick-precision
        - (signed type)((unsigned type)now - (unsigned type)expire) > 0

YAMAMOTO Takashi

> 
> -- 
> Emmanuel Dreyfus
> http://hcpnet.free.fr/pubz
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