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From: Lukas Czerner <lczerner@redhat.com>
To: Karel Zak <kzak@redhat.com>
Cc: util-linux@vger.kernel.org
Subject: Re: [PATCH] blkdiscard: Refuse to proceed if signatures are found
Date: Thu, 18 Jun 2020 12:33:27 +0200
Message-ID: <20200618103327.o64jhcboobwpnr4a@work> (raw)
In-Reply-To: <20200618100626.f5uyuxomfhbnhibn@ws.net.home>

On Thu, Jun 18, 2020 at 12:06:26PM +0200, Karel Zak wrote:
> On Thu, Jun 18, 2020 at 11:29:16AM +0200, Lukas Czerner wrote:
> > With this commit blkdiscard will check for existing signatures on the
> > device and refuse to continue if any are found unless the operation is
> > forced with the -f option.
> 
> Good idea.
> 
> > +/*
> > + * Check existing signature on the open fd
> > + * Returns	0  if no signature was found
> > + * 		1  if a signature was found
> 
> this is not true, 0 means detected, 1 not found
> 
> > + * 		<0 on error
> > + */
> > +static int device_empty(int fd, char *path)
> 
> This is difficult for to read, at first glance it seems according
> to function name that 1 means "yes, it's empty".
>       
> Maybe rename it to probe_device().
> 
> > +{
> > +	const char *type;
> > +	blkid_probe pr = NULL;
> > +	int ret = -1;
> > +
> > +	pr = blkid_new_probe();
> > +	if (!pr || blkid_probe_set_device(pr, fd, 0, 0))
> > +		return ret;
> > +
> > +	blkid_probe_enable_superblocks(pr, TRUE);
> > +	blkid_probe_enable_partitions(pr, TRUE);
> > +
> > +	ret = blkid_do_fullprobe(pr);
> > +	if (ret)
> > +		return ret;
> 
> yes, blkid_do_fullprobe() returns: 0 on success, 1 if nothing is detected or -1 on case of error.
> 
> > +
> > +	if (!blkid_probe_lookup_value(pr, "TYPE", &type, NULL)) {
> > +		warnx("%s contains existing file system (%s).",path ,type);
> > +	} else if (!blkid_probe_lookup_value(pr, "PTTYPE", &type, NULL)) {
> > +		warnx("%s contains existing partition (%s).",path ,type);
> > +	} else {
> > +		warnx("%s contains existing signature.", path);
> > +	}
> > +
> > +	blkid_free_probe(pr);
> > +	return ret;
> 
> This is always 0.
> 
> > +}
> >  
> >  int main(int argc, char **argv)
> >  {
> >  	char *path;
> > -	int c, fd, verbose = 0, secsize, force = 0;
> > +	int c, fd, ret, verbose = 0, secsize, force = 0;
> >  	uint64_t end, blksize, step, range[2], stats[2];
> >  	struct stat sb;
> >  	struct timeval now, last;
> > @@ -184,7 +219,7 @@ int main(int argc, char **argv)
> >  		errtryhelp(EXIT_FAILURE);
> >  	}
> >  
> > -	fd = open(path, O_WRONLY | (force ? 0 : O_EXCL));
> > +	fd = open(path, O_RDWR | (force ? 0 : O_EXCL));
> >  	if (fd < 0)
> >  		err(EXIT_FAILURE, _("cannot open %s"), path);
> >  
> > @@ -217,6 +252,21 @@ int main(int argc, char **argv)
> >  		errx(EXIT_FAILURE, _("%s: length %" PRIu64 " is not aligned "
> >  			 "to sector size %i"), path, range[1], secsize);
> >  
> > +	 /* Check for existing signatures on the device */
> > +	if ((ret = device_empty(fd, path)) == 0) {
> 
>  What about:
> 
>  switch (probe_device(fd, path)) {
>  case 0: /* signature detected */
> > +		/*
> > +		 * Only require force in interactive mode to avoid
> > +		 * breaking existing scripts
> > +		 */
> > +		if (!force && isatty(STDIN_FILENO)) {
> > +			errx(EXIT_FAILURE,
> > +			     _("This is destructive operation, data will " \
> > +			       "be lost! Use the -f option to override."));
> > +		}
> > +		warnx(_("Operation forced, data will be lost!"));
>         break;
> 
>  case 1: /* no signature */
>         break;
> 
>  default: /* error */
> > +		err(EXIT_FAILURE, _("failed to probe the device"));
>         break;
>  }
> 
> 
> I think it's more readable ;-)

Sure, I can do that. The bad comment definitelly makes it more confusing
that it needed to be :)

if (!device_empty()) was the intention but then I still have to deal
with the error. I'll do the switch change.

-Lukas

> 
>     Karel
> 
> -- 
>  Karel Zak  <kzak@redhat.com>
>  http://karelzak.blogspot.com


      reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-18  9:29 Lukas Czerner
2020-06-18 10:06 ` Karel Zak
2020-06-18 10:33   ` Lukas Czerner [this message]

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