Jan -
Thanks for the feedback.
On 8/9/19 8:05 AM, Jan Kara wrote:
On Wed 07-08-19 08:32:58, Steven J. Magnani wrote:
From: Steve Magnani <steve@xxxxxxxxxxxxxxx>
Windows is capable of creating UDF files having named streams.
One example is the "Zone.Identifier" stream attached automatically
to files downloaded from a network. See:
https://msdn.microsoft.com/en-us/library/dn392609.aspx
Modification of a file having one or more named streams in Linux causes
the stream directory to become detached from the file, essentially leaking
all blocks pertaining to the file's streams. Worse, an attempt to delete
the file causes its directory entry (FID) to be deleted, but because the
driver believes that a hard link to the file remains, the Extended File
Entry (EFE) and all extents of the file itself remain allocated. Since
there is no hard link, after the FID has been deleted all of these blocks
are unreachable (leaked).
...
For this case, this partial solution reduces the number of blocks leaked
during file deletion to just one (the EFE containing the stream data).
Thanks for the patch! I was thinking about this and rather than this
partial fix, I'd prefer to fail the last unlink of an inode with
a named-stream directory with EOPNOTSUPP. Later we can properly handle this
and walk the named-stream directory and remove all associated EFEs for the
named streams. After all named-stream directories are restricted to not
have any subdirectories, hardlinks, or anything similarly fancy so the walk
should not be *that* hard to implement.
Maybe not but it's more work than I am able to take on anytime soon.
Absent a complete solution, how to handle this is a judgement call.
Since Windows seems to attach a Zone.Identifier stream to _all_ files
downloaded from a network, and since interchange between Windows and Linux
via USB Mass Storage is a somewhat common (or at least desirable) use case
for UDF, this issue seemed fairly serious from a user perspective. Leaking
all the blocks of a file on delete is pretty bad. Leaking a single block is
still bad, but much less so. One could argue that prohibiting deletion of
files with named streams is nearly as bad as leaking all the blocks - in
both cases, within Linux, none of the file's blocks can be reused.
That's pretty limiting for users. It's too limiting for my use cases.
------------------------------------------------------------------------
Steven J. Magnani "I claim this network for MARS!
www.digidescorp.com Earthling, return my space modulator!"
#include <standard.disclaimer>
