[Info-vax] 64-bit file sizes, was: Re: scp or sftp: file is "raw", needs to be parsed - possible to work around that?

[Arne Vajhøj]

On 5/20/2021 1:59 PM, Simon Clubley wrote:
> On 2021-05-20, Stephen Hoffman <seaohveh at hoffmanlabs.invalid> wrote:
>> And now I'm pondering what the eventual advent of 64-bit file sizes
>> will do to existing apps and APIs...
> 
> That's a good question.
> 
> It's a pity that on VMS, when using the VMS APIs instead of the C ones,
> you can't just use a 64-bit version of stat() with appropriate 64-bit
> integer variables, compile your code, and then call it a day. :-(
> 
> I wonder if sizes will be locked at the current maximum size for the
> older APIs (with the value varying depending on whether you are working
> in blocks or bytes) with yet _another_ set of APIs to get and manipulate
> the 64-bit file size.
> 
> It's also possible that when using higher-level languages such as C
> with the C APIs they may just do what Linux does and just call
> different versions in the glibc stat() call depending on whether you
> are working with 32-bit or 64-bit variables.
> 
> That might not work however due to the fact that you can have both
> 32-bit and 64-bit pointers in the same image on VMS, unlike the either
> 32-bit or 64-bit pointers seen in Linux binaries.

VMS C stat can switch between 32 and 64 bit st_size just by recompiling
with _LARGEFILE defined.

It is not a problem with mixed 32 and 64 bit pointers as stat is calling
different functions depending on the define.

(DECC$__LONG_GID_STAT and DECC$__OFF64_LONG_GID_STAT)

The VMS API's does not have a 2 GB or 4 GB problem as they
count in blocks not bytes.

So the 32 bit field limit size to 1 TB or 2 TB.

Which is fundamentally the same problem, but in practice a 2 GB
limit is much more problematic than a 1 TB limit.

And since ODS-5 is limited to 1 TB anyway then no bigger files
exist on VMS today.

When we get ODS-n n>5 based on GFS-2 allowing PB and EB
files then some changes will be needed.

Maybe we will have XABFHCL with XAB$Q_EBK and RAB64L with
more RAB$W_RFA.

:-)

> Also, will there need to be another version of RMS indexed files to
> handle the larger file sizes ?

Or maybe they will limit index-sequential files to 1 TB and
say that for >1TB then people have to use SQLite (which
funny enough is currently limited to 256 TB due to 32 bit
page indexes and 64 KB pages).

Arne