[Qemu-devel] Re: [PATCH] rev5: support colon in filenames

[Jan Kiszka <jan.kiszka@siemens.com>]

Ram Pai wrote:
> Problem: It is impossible to feed filenames with the character colon because
> qemu interprets such names as a protocol. For example filename scsi:0, is
> interpreted as a protocol by name "scsi".
> 
> This patch allows user to espace colon characters. For example the above
> filename can now be expressed either as 'scsi\:0' or as file:scsi:0
> 
> anything following the "file:" tag is interpreted verbatin. However if "file:"
> tag is omitted then any colon characters in the string must be escaped using
> backslash.
> 
> Here are couple of examples:
> 
> scsi\:0\:abc is a local file scsi:0:abc
> http\://myweb is a local file by name http://myweb
> file:scsi:0:abc is a local file scsi:0:abc
> file:http://myweb is a local file by name http://myweb
> 
> fat:c:\path\to\dir\:floppy\:  is a fat file by name \path\to\dir:floppy:
> NOTE:The above example cannot be expressed using the "file:" protocol.
> 
> 
> Changelog w.r.t to iteration 0:
>    1) removes flexibility added to nbd semantics  eg -- nbd:\::9999
>    2) introduce the file: protocol to indicate local file
> 
> Changelog w.r.t to iteration 1:
>    1) generically handles 'file:' protocol in find_protocol
>    2) centralizes 'filename' pruning before the call to open().
>    3) fixes buffer overflow seen in fill_token()
>    4) adheres to codying style
>    5) patch against upstream qemu tree
> 
> Changelog w.r.t to iteration 2:
>    1) really really fixes buffer overflow seen in 
> 	fill_token() (if not, beat me :)
>    2) the centralized 'filename' pruning had a side effect with
> 	qcow2 files and other files. Fixed it. _open() is back.
> 
> Changelog w.r.t to iteration 3:
>    1) support added to raw-win32.c (i do not have the setup to 
> 		test this change. Request help with testing)
>    2) ability to espace option-values containing commas using 
> 	backslashes 
> 	eg  file=file:abc,,  can also be expressed as file=file:abc\, 
> 		where 'abc,' is a filename
>    3) fixes a bug (reported by Jan Kiszka) w.r.t support for -snapshot

Yep, that's fixed in this version.

>    4) renamed _open() to qemu_open() and removed dependency on PATH_MAX
> 
> Changelog w.r.t to iteration 4:
>    1) applies to upstream qemu and qemu-kvm tree
>    
> 
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> 
> 
>  block.c               |   30 +++-------------
>  block/raw-posix.c     |   35 ++++++++++++++----
>  block/raw-win32.c     |   26 ++++++++++++--
>  block/vvfat.c         |   97 ++++++++++++++++++++++++++++++++++++++++++++++++-
>  cutils.c              |   26 +++++++++++++
>  qemu-common.h         |    1 +
>  qemu-option.c         |    8 ++++-
>  8 files changed, 185 insertions(+), 38 deletions(-)
> 
> diff --git a/block.c b/block.c

...

> @@ -359,25 +351,15 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
>          }
>          total_size = bdrv_getlength(bs1) >> SECTOR_BITS;
>  
> -        if (bs1->drv && bs1->drv->protocol_name)
> -            is_protocol = 1;
> -
>          bdrv_delete(bs1);
>  
>          get_tmp_filename(tmp_filename, sizeof(tmp_filename));
>  
> -        /* Real path is meaningless for protocols */
> -        if (is_protocol)
> -            snprintf(backing_filename, sizeof(backing_filename),
> -                     "%s", filename);
> -        else
> -            realpath(filename, backing_filename);
> -

This removes realpath without any replacement, right? Did you verify
that this doesn't break anything, namely snapshots with relative paths
for the backing image? Please check commit a817d93 and provide a
reasoning why it's safe to drop it.

Jan

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