Patricks blob dir perm

[jimfulton]

This makes it easier to share blob cache dirs, for example when you want to access the database as a normal user and share the cache with a app server process running as a special user.

[jimfulton]

This introduces a backward incompatibility. ZODB.tests.testblob.storage_reusable_suite now requires a factory with a different signature. This means unmodified blob storage implementations will have their tests broken.

I'm guessing that this would effect relstorage and neo, although I'm not positive.

To be safe, we should:

• Move the tests for permission setting into a separate test that isn't included in storage_reusable_suite, and
• Add storage_reusable_suite2 that has the new factory signature that includes the tests provided by storage_reusable_suite as well as the permission test.

Also, a point of style. Please don't do:

some_long_function_name(foo,
    bar)

Instead, do:

some_long_function_name(foo,
                        bar)

or:

some_long_function_name(
    foo, bar)

[vpelletier]

This incompatibility won't be a problem for neo because it still lacks blob support.
Jim: Thanks a lot for notifying me of the change.

[tseaver]

@hathawsh Can you figure out if / how Relstorage would be affected?

[jamadden]

@jimfulton @tseaver I don't think RelStorage would be affected. It doesn't use ZODB's storage_reusable_suite as far as I can see, it has its own copy. It also doesn't directly use ZODB.blob.BlobStorage.

[jimfulton]

Thanks. (I was going to figure this out myself, now that I'm practically a RelStorage expert. ;))

I'll freshen this PR soon (unless someone beats me to it, of course).

[jimfulton]

Well, the merge with master didn't go well. Still lots of rot.

[jimfulton]

Stepping back

This change was pretty conservative. It kept existing behaviour and provided a way to override it. This was nobley backward compatible.

However, I think everyone (who pays attention) agrees that the existing behavior is stupid. I propose we simply change the behavior to not specify permissions when creating blob files and directories and let users control this the way they control permissions of other files (e.g. umask)

[jimfulton]

Closing in favor of #156