Re: Max. number of subdirectories dump

[Johnny Billquist <bqt%softjar.se@localhost>]

On 2013-08-19 08:41, David Holland wrote:
> On Sun, Aug 18, 2013 at 06:04:55PM +0200, Johnny Billquist wrote:
>   > Looking at 2.11BSD, it looks like this:
>   >
>   > struct  direct {
>   > [snip]
>   >
>   > In NetBSD (fairly current):
>   >
>   > struct dirent {
>
> careful, you want struct direct, not struct dirent:

Hmm. Probably a good point. I was wondering if NetBSD had just renamed 
direct to dirent, but that was just me getting confused then. (And lazy, 
since I didn't really search around, which I should have, but the rest 
matched so well. :-) )

However...

> struct  direct {
>          u_int32_t d_fileno;             /* inode number of entry */
>          u_int16_t d_reclen;             /* length of this record */
>          u_int8_t  d_type;               /* file type, see below */
>          u_int8_t  d_namlen;             /* length of string in d_name */
>          char      d_name[FFS_MAXNAMLEN + 1];/* name with length <= 
> FFS_MAXNAMLEN */
> };
>
> not that it's actually much different.

I was reading the manpage on dirent for NetBSD 3 previously, and it 
looked like that as well. Obviously, for this, FFS_MAXNAMLEN must be 255 
or less...
(Well, ok, it can be larger, but the actual name stored in d_name will 
not be more than 255 characters anyway...)

That was part of the reason that even triggered me to check somewhat 
current sources.

>   > It's an obvious optimization to keep type already in the directory
>   > itself. But is there any other reason why it was added there?
>
> Speed. There's a moderately famous paper "A trace-driven analysis of
> the UNIX 4.2 BSD file system" -- you might have heard of it :-)

Actually I haven't. I should look it up. Thanks.
And speed was the obvious optimization that I was thinking of. 
(Apparently not so obvious, so I should learn to not write such things.)

        Johnny

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Johnny Billquist                  || "I'm on a bus
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