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Fix MkdirAll* and its usage #629

Merged
merged 2 commits into from
May 18, 2020
Merged

Fix MkdirAll* and its usage #629

merged 2 commits into from
May 18, 2020

Commits on May 18, 2020

  1. idtools/mkdirAs: error out if dir exists as file 

    os.MkdirAll() function returns "not a directory" error in case a
directory to be created already exists but is not a directory
(e.g. a file). MkdirAllNewAs function do not replicate the behavior.

This is a bug since it is expected to ensure the required directory
exists and is indeed a directory, and return an error otherwise.

Signed-off-by: Kir Kolyshkin <[email protected]>
    @kolyshkin
    kolyshkin committed May 18, 2020
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  2. Fix MkdirAll usage 

    This subtle bug keeps lurking in because error checking for `Mkdir()`
and `MkdirAll()` is slightly different wrt `EEXIST`/`IsExist`:

 - for `Mkdir()`, `IsExist` error should (usually) be ignored
   (unless you want to make sure directory was not there before)
   as it means "the destination directory was already there";

 - for `MkdirAll()`, `IsExist` error should NEVER be ignored.

This commit removes ignoring the IsExist error, as it should not
be ignored.

For more details, a quote from my opencontainers/runc#162 (July 2015):

-quote-

TL;DR: check for IsExist(err) after a failed MkdirAll() is both
redundant and wrong -- so two reasons to remove it.

Quoting MkdirAll documentation:

MkdirAll creates a directory named path, along with any necessary
parents, and returns nil, or else returns an error. If path
is already a directory, MkdirAll does nothing and returns nil.

This means two things:

If a directory to be created already exists, no error is
returned.

If the error returned is IsExist (EEXIST), it means there exists
a non-directory with the same name as MkdirAll need to use for
directory. Example: we want to MkdirAll("a/b"), but file "a"
(or "a/b") already exists, so MkdirAll fails.

The above is a theory, based on quoted documentation and my UNIX
knowledge.

In practice, though, current MkdirAll implementation [1] returns
ENOTDIR in most of cases described in containers#2, with the exception when
there is a race between MkdirAll and someone else creating the
last component of MkdirAll argument as a file. In this very case
MkdirAll() will indeed return EEXIST.
Because of containers#1, IsExist check after MkdirAll is not needed.

Because of containers#2 and containers#3, ignoring IsExist error is just plain wrong,
as directory we require is not created. It's cleaner to report
the error now.

Note this error is all over the tree, I guess due to copy-paste,
or trying to follow the same usage pattern as for Mkdir(),
or some not quite correct examples on the Internet.

[1] https://github.com/golang/go/blob/f9ed2f75/src/os/path.go

-end-quote-

Signed-off-by: Kir Kolyshkin <[email protected]>
    @kolyshkin
    kolyshkin committed May 18, 2020
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