Re: [Qemu-devel] [PATCH v4 1/4] block: introducing 'bdrv_co_delete_file' interface

[Kevin Wolf]

Am 06.08.2019 um 15:27 hat Daniel Henrique Barboza geschrieben:
> > > diff --git a/block.c b/block.c
> > > index c139540f2b..6e2b0f528d 100644
> > > --- a/block.c
> > > +++ b/block.c
> > > @@ -621,6 +621,17 @@ int get_tmp_filename(char *filename, int size)
> > >   #endif
> > >   }
> > > +/**
> > > + * Helper that checks if a given string represents a regular
> > > + * local file.
> > > + */
> > > +bool bdrv_path_is_regular_file(const char *path)
> > > +{
> > > +    struct stat st;
> > > +
> > > +    return (stat(path, &st) == 0) && S_ISREG(st.st_mode);
> > > +}
> > > +
> > >   /*
> > >    * Detect host devices. By convention, /dev/cdrom[N] is always
> > >    * recognized as a host CDROM.
> > This hunk isn't generic, it belong in file-posix.c
> 
> Patch 3 uses this function as part of the core logic of this fix (do not
> delete the file if the file already existed) inside block/cryptoc. This
> is the reason it is exposed here. I assumed that we do not want a
> public function inside file-posix.c (since there is none - everything
> is done using the BD interfaces).

Hm... This doesn't feel right. crypto can't assume that it's working on
a local file. It's working on some lower level BlockDriverState,
whatever that may be. Remember that you could pass all kind of URLs e.g.
for network protocols like NBD or gluster. You don't want to check
whether a local filename exists then.

In fact, I'm not sure if having a special case for an already existing
file is even worth it: By the time we fail, we'll already have truncated
the file, so the old data is lost anyway. Deleting that empty or
half-initialised file doesn't seem much worse than leaving a broken file
behind.

Kevin