[vbox-dev] [Patch] Fix shared folder rewinddir() failure with guest Linux kernel >= 2.6.37

[Frank Mehnert]

Paul,

On Saturday 13 August 2011 16:02:01 Paul Mitchell wrote:
> Calls to rewinddir() on shared folder directory fds silently fail with
> kernel 2.6.37 and later. This patch to the vboxsf driver restores the
> pre-2.6.37 behaviour.
> 
> For background details see "change default_llseek action" at
> http://lwn.net/Articles/405097/ The change was released with kernel
> 2.6.37, commit 776c163b1b93c8dfa5edba885bc2bfbc2d228a5f PHP bug #55364 is
> symptomatic, see https://bugs.php.net/bug.php?id=55364
> 
> This test program checks that a call to readdir returns the same entry
> after rewinddir() as one does after opendir(). Userspace is Ubuntu 10.04.3
> LTS.
> 
> #include <sys/types.h>
> #include <dirent.h>
> 
> void test_rewinddir( const char *path ) {
>     struct dirent *e1, *e2;
>     DIR *d = opendir( path );
>     e1 = readdir( d );
>     rewinddir( d );
>     e2 = readdir( d );
>     closedir( d );
> 
>     if( e1 == 0 ) return;
>     puts( e2 && 0 == strcmp( e1->d_name, e2->d_name )
>           ? "OK" : "FAIL" );
> }
> 
> void main( int argc, const char **argv ) {
>     while( --argc ) {
> 	puts( argv[argc] );
> 	test_rewinddir( argv[argc] );
>     }
> }
> 
> With the unpatched vboxsf driver on Linux kernel >= 2.6.37, the test will
> fail for a shared folder, indicating that rewinddir failed. Running under
> strace, a lseek syscall for the directory fd can be seen to fail with
> ESPIPE - the new default llseek behaviour.
> 
> With the patch to vboxsf on kernel >= 2.6.37, behaviour reverts to normal.
> 
> MIT licensed.
> 
> Index: src/VBox/Additions/linux/sharedfolders/dirops.c
> ===================================================================
> --- src/VBox/Additions/linux/sharedfolders/dirops.c	(revision 38435)
> +++ src/VBox/Additions/linux/sharedfolders/dirops.c	(working copy)
> @@ -292,6 +292,9 @@
>      .readdir = sf_dir_read,
>      .release = sf_dir_release,
>      .read    = generic_read_dir
> +#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 37)
> +  , .llseek  = generic_file_llseek
> +#endif
>  };

problem and fix confirmed. Thank you very much for the report, the
testcase and the fix!

Kind regards,

Frank
-- 
Dr.-Ing. Frank Mehnert
Senior Manager Software Development Desktop Virtualization, VirtualBox
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