Re: [Qemu-devel] [PATCH] hw/9pfs/virtio-9p-local.c: use snprintf() instead of sprintf()

[Eric Blake <eblake@redhat.com>]

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On 02/04/2014 05:25 AM, Markus Armbruster wrote:

> Second guessing when a pathname is too long for a system call is not a
> good idea.  If it's too long, the system call will tell you.  As Dan
> noted, PATH_MAX is *not* a hard limit.
> 
>     {PATH_MAX}
>         Maximum number of bytes the implementation will store as a
>         pathname in a user-supplied buffer of unspecified size,
>         including the terminating null character. Minimum number the
>         implementation will accept as the maximum number of bytes in a
>         pathname.

Linux allows unbelievably long absolute names.  Jim Meyering proved with
coreutils that you can create an absolute name well over a megabyte in
length.  The trick is that you have to access it via relative names
where each relative name is PATH_MAX or less (that is, the Linux kernel
refuses to operate on more than a page at a time when doing file name
resolution), by using openat() and friends.  mkdirat() can create a
directory with an absolute name longer than PATH_MAX, even if mkdir() can't.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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