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Simplify and fix os.MkdirAll() usage

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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 #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.

[v2: a separate aufs commit is merged into this one]

[1] f9ed2f75/src/os/path.go

Signed-off-by: Kir Kolyshkin <kir@openvz.org>
This commit is contained in:
Kir Kolyshkin 2015-07-29 16:49:05 -07:00
parent 9f198e9313
commit fe45bb6d4d
1 changed files with 2 additions and 2 deletions
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4
archive/archive.go
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@ -714,7 +714,7 @@ func (archiver *Archiver) CopyWithTar(src, dst string) error {
}
// Create dst, copy src's content into it
logrus.Debugf("Creating dest directory: %s", dst)
if err := system.MkdirAll(dst, 0755); err != nil && !os.IsExist(err) {
if err := system.MkdirAll(dst, 0755); err != nil {
return err
}
logrus.Debugf("Calling TarUntar(%s, %s)", src, dst)
@ -746,7 +746,7 @@ func (archiver *Archiver) CopyFileWithTar(src, dst string) (err error) {
dst = filepath.Join(dst, filepath.Base(src))
}
// Create the holding directory if necessary
if err := system.MkdirAll(filepath.Dir(dst), 0700); err != nil && !os.IsExist(err) {
if err := system.MkdirAll(filepath.Dir(dst), 0700); err != nil {
return err
}