[Libguestfs] [PATCH 1/3] New API: case-sensitive-path to return case sensitive path on NTFS 3g fs

[Matthew Booth]

On 26/10/09 11:08, Richard W.M. Jones wrote:
>>> +  size_t next = 1;
>>> +
>>> +  /* MUST chdir ("/") before leaving this function. */
>>> +  if (chdir (sysroot) == -1) {
>>> +    reply_with_perror ("%s", sysroot);
>>> +    return NULL;
>>> +  }
>>
>> I'm not convinced chdir is necessary in this function if you use
>> openat() throughout.
>
> I'm pretty sure I need opendirat to make this work, and that function
> doesn't seem to exist (checked on Fedora 11).

You only need openat() followed by fdopendir().

>> This API seems like an unfortunate pimple. Would it not be better to
>> *not* export this API, and instead call this automatically everywhere
>> the daemon opens a file on ntfs?
>
> But how does it know what the underlying filesystem is up to?  I agree
> it's a bug in NTFS 3g, but changing all the code to do very expensive
> magic doesn't seem like the right way, and you can't detect which
> filesystems are broken like this.

Problem is, if you don't put the magic in you're pushing the problem on 
to the library user. The code's going to look pretty much the same every 
time, so it might as well be in the library. You could take 2 approaches 
here:

1. Always use case-sensitive-path: slow, but should be safe.
2. Detect fs type and call case-sensitive-path as required: probably 
tricky to get absolutely right (think: ntfs mounted as an additional 
volume under /mnt/windows).

I'd go for 1. It should be safe, and it's not as if the slowness is 
likely to be noticeable here.

Matt
-- 
Matthew Booth, RHCA, RHCSS
Red Hat Engineering, Virtualisation Team

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