Fix MkdirAll* and its usage #35618
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Fix MkdirAll* and its usage #35618
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Standard golang's `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). Our own `idtools.MkdirAs*()` functions do not replicate the behavior. This is a bug since all `Mkdir()`-like functions are expected to ensure the required directory exists and is indeed a directory, and return an error otherwise. As the code is using our in-house `system.Stat()` call returning a type which is incompatible with that of golang's `os.Stat()`, I had to amend the `system` package with `IsDir()`. A test case is also provided. Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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Also /cc @salah-khan (because the same changes may be needed for the Windows side as well if we start supporting actual |
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@kolyshkin looks like there's some lint errors; |
This subtle bug keeps lurking in because error checking for `Mkdir()`
and `MkdirAll()` is slightly different wrt to `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.
Mostly, this commit just removes ignoring the IsExist error, as it
should not be ignored.
Also, there are a couple of cases then IsExist is handled as
"directory already exist" which is wrong. As a result, some code
that never worked as intended is now removed.
NOTE that `idtools.MkdirAndChown()` behaves like `os.MkdirAll()`
rather than `os.Mkdir()` -- so its description is amended accordingly,
and its usage is handled as such (i.e. IsExist error is not ignored).
For more details, a quote from my runc commit 6f82d4b (July 2015):
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:
1. If a directory to be created already exists, no error is
returned.
2. 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.
3. In practice, though, current MkdirAll implementation [1] returns
ENOTDIR in most of cases described in #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 #1, IsExist check after MkdirAll is not needed.
Because of #2 and moby#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
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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LGTM |
This was referenced May 16, 2020
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- What I did
idtools.Mkdir*functions to return an error if a directory to be created already exists but is not a directory.MkdirAll*functions to not ignoreIsExisterrors.Please see commit messages for details.
- How I did it
Manually checked all the code paths using MkdirAll and idtools.Mkdir functions.
- How to verify it
For idtools.Mkdir*, there is a test case included.
- Description for the changelog
- A picture of a cute animal (not mandatory but encouraged)