[dm-devel] dm-flakey NOT to return -EIO on READ?

[Lukas Herbolt]

Hi,
Yes this part is wrong and reads are not dropped.
I have a patch ready, just have to send it out.

Lukas

On Wed, Jul 6, 2016 at 8:33 AM, Akira Hayakawa <ruby.wktk at gmail.com> wrote:

> Hi,
>
> I am using dm-flakey to emulate a broken device that should return -EIO on
> both read and write.
> I use the parameter up_interval=0 and down_interval=1.
>
> But when I am dd-ing the flakey device, while write fails, read succeeds.
> This isn't the behavior I expect.
>
> Then I looked into the code.
>
> 326 static int flakey_end_io(struct dm_target *ti, struct bio *bio, int
> error)
> 327 {
> 328         struct flakey_c *fc = ti->private;
> 329         struct per_bio_data *pb = dm_per_bio_data(bio, sizeof(struct
> per_bio_data));
> 330
> 331         /*
> 332          * Corrupt successful READs while in down state.
> 333          * If flags were specified, only corrupt those that match.
> 334          */
> 335         if (fc->corrupt_bio_byte && !error && pb->bio_submitted &&
> 336             (bio_data_dir(bio) == READ) && (fc->corrupt_bio_rw ==
> READ) &&
> 337             all_corrupt_bio_flags_match(bio, fc))
> 338                 corrupt_bio_data(bio, fc);
> 339
> 340         return error;
> 341 }
>
> When the bio direction is READ and currupt_bio_bytes isn't specified
> the READ bio is handled normally right?
>
> I think READ requests should return -EIO if
>
> 1. corrupt_bio_bytes isn't specified
> 2. but the requested is handled during down interval.
>
> as well as WRITE requests:
>
> 305                 /*
> 306                  * Corrupt matching writes.
> 307                  */
> 308                 if (fc->corrupt_bio_byte && (fc->corrupt_bio_rw ==
> WRITE)) {
> 309                         if (all_corrupt_bio_flags_match(bio, fc))
> 310                                 corrupt_bio_data(bio, fc);
> 311                         goto map_bio;
> 312                 }
> 313
> 314                 /*
> 315                  * By default, error all I/O.
> 316                  */
> 317                 return -EIO;
> 318         }
>
> This code is similar to what we see in the end_io.
>
> If my understanding is correct, I would like to modify dm-flakey to return
> -EIO in the end_io.
>
> I would like to request for comments.
>
> Thanks,
>
> - Akira
>
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>



-- 
Lukas Herbolt
RHCE, RH436, BSc, SSc
Senior Technical Support Engineer
Global Support Services (GSS)
Email:    lherbolt at redhat.com
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