Re: old bug: mount_nfs path/name is limited to 88 chars

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On 01/19/15 13:20, Garrett Cooper wrote:
> On Jan 19, 2015, at 8:46, Brandon Allbery <allbery.b_at_gmail.com>
> wrote:
> 
>> On Mon, Jan 19, 2015 at 10:44 AM, Anton Shterenlikht
>> <mexas_at_bris.ac.uk> wrote:
>> 
>>> So perhaps changing MNAMELEN will break statfs(2) on -stable
>>> too?
>>> 
>> 
>> I believe the context there is not so much "-current is special",
>> as "changing it for everyone is bad news" (and this would
>> necessarily need to originate in -current).
> 
> A compat layer needs to be created for all of the affected
> syscalls, and the change needs to be made. That’s it in a
> nutshell.
> 
> Doing it in 11 makes sense since there is a compat layer for 10
> now… if I knew all of the steps I would happily do them as annoys
> me from time to time as well with the path length issue.

Compat layer may break applications in other funny ways and we
probably have to return e.g. ENAMETOOLONG for legacy applications if
the names are too long to fit into the buffer, but I don't see any
easy solution either: I wish we have bumped it in 2003 when the struct
receives its first big revamp by bumping all statistic fields to 64-bit.

I personally think we probably better create a new API and keep the
existing one for (limited) compatibility.  For instance, it may be
sensible to make f_mntfromname and f_mntonname fields variable length
and have the caller pass a pointer and their length.  If we set an
arbitrary limit, no matter it's 88, 256 or 4096, one will hit it some
time.

BTW. If someone wants to change statfs(2), please make sure to create
reverse-compatibility shims at the same time (see lib/libc/sys/fcntl.c
for an example).  The statfs(2) API is used in a lot of places,
especially fts(3), and breaking it either way (running new world with
old kernel, or running old world with new kernel) would be a big pain
to recover from.

Cheers,
- -- 
Xin LI <delphij_at_delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die
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