Re: MAXNAMLEN vs NAME_MAX

[christos%zoulas.com@localhost (Christos Zoulas)]

On Sep 27,  3:48pm, kre%munnari.OZ.AU@localhost (Robert Elz) wrote:
-- Subject: Re: MAXNAMLEN vs NAME_MAX

|     Date:        Mon, 26 Sep 2011 09:46:09 -0400
|     From:        christos%zoulas.com@localhost (Christos Zoulas)
|     Message-ID:  <20110926134609.8322A9711D%rebar.astron.com@localhost>
| 
|   | But it is better long term to move forward and allow for longer
|   | names.
| 
| Why?
| 
| Certainly the original 14 byte limit was occasionally a nuisance (but
| even that was better than 8+3 which was typical), but longer than 255?
| 
| Even using a utf-8 encoded filename, at 5 bytes/character, that's still
| a 51 character filename, which is longer than rational - names >= 40
| characters mean that on a standard 80 column display, ls can't even show
| 2 columns of names.

Heh.

| The 255 limit was just because that's how many bytes a one byte length
| field permitted, not because anyone thought names that long made sense.
| But if you're going to increase it, why  stop at 511?  That number
| means nothing - the next logical limit would be 65535 wouldn't it?

Eats too much space on the stack I think.

| 511 is already too big to keep directory entries within one disc block
| when using small blocks, so you've already lost the idempotent directory
| entry write feature that was part of the original design (both v7fs and
| ffs) (not just file system block writes, but actual drive writing, you
| can't fix this just by making a larger minimum frag size, only by changing
| drive electronics and/or microcode).

I think we are already moving away from 512 byte sectors...

Anyway this is optional, most filesystems only can support upt to 255 byte
filenames as others have pointed out. There was also a mess about the use
of MAXNAMLEN vs. NAME_MAX in the kernel which I have fixed now in the following
way:

1. Each filesystem defines its own FS_MAXNAMLEN and uses it to advertise its
   own limit.
2. MAXNAMLEN == NAME_MAX == 511 as the maximum limit supported.
3. KERNEL_NAME_MAX == 255 is the current internal limit of what the kernel
   will return to userland for all filesystems.

christos