Re: [PATCH] Ignore symlink traversal failures in grub-mount readdir

[Vladimir 'φ-coder/phcoder' Serbinenko]

On 10.03.2013 14:01, Vladimir 'φ-coder/phcoder' Serbinenko wrote:

> On 09.03.2013 17:47, Andrey Borzenkov wrote:
> 
>> В Fri, 12 Oct 2012 17:09:54 +0100
>> Colin Watson <address@hidden> пишет:
>>
>>> This is very much a temporary hack, so I'm sending it here for
>>> discussion rather than just committing it even though it's quite simple.
>>>
>>> r3036.1.15 introduced support for filling in the attributes of files in
>>> fuse_readdir.  However, symlinks to directories are passed to call_fill
>>> with info.dir unset; call_fill will then try to open them with
>>> grub_file_open, and get GRUB_ERR_BAD_FILE_TYPE because it's ultimately a
>>> directory not a regular file.  It then causes the whole readdir call to
>>> fail.  The net effect is that if you, for example, have a symlink
>>> anywhere in the top level of a filesystem, then the entire filesystem
>>> appears empty in grub-mount.  This is the root cause of
>>> https://bugs.launchpad.net/bugs/1051306.
>>>
>>> I think that the proper solution is to pass the full
>>> grub_fshelp_filetype to dirhook functions, which would permit
>>> implementing true symlink support in grub-mount.  That would be a fairly
>>> large change that I don't have time for at the moment.  As a stopgap, I
>>> suggest that we ignore errors from individual grub_file_open calls
>>> during fuse_readdir.  How does this patch look?
>>>
>>
>> The only reason to call grub_file_open() is to fetch file size, and file
>> size is already available when hooks are called. So what about patch
>> below? It fixes problem for me, and it trivial enough. This allows
>> directory listing to work again. I can extend it with info.is_link to
>> return proper filetype to FUSE, but implementing full support needs
>> adding readlink that is a separate topic.
>>
>> I tested it with ext4 and cpio and it works. Testing on more systems
>> (in particular, NTFS, which is the only one with non-trivial change) is
>> appreciated.
>>
> 
> Some time ago I made a similar patch but for another motivation: current
> code is way too inefficient for large directories as you have to rescan
> directory for every file. The problem with this patch is 10 bytes
> increase of core.img. This may be acceptable given this problem (it
> happens in ls on runtime as well) and inefficency of scanning.
>

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