[OE-core] [PATCH 1/2] image.py: avoid mkdir race when building multiple images

[Richard Purdie]

On Thu, 2015-11-19 at 11:20 +0000, Mike Crowe wrote:
> If multiple images are being built simultaneously against the same
> sysroot then the call to os.makedirs in Image._write_wic_env can fail
> with:
> 
> File: '.../meta/lib/oe/image.py', lineno: 341, function: _write_wic_env
>      0337:        """
>      0338:        stdir = self.d.getVar('STAGING_DIR_TARGET', True)
>      0339:        outdir = os.path.join(stdir, 'imgdata')
>      0340:        if not os.path.exists(outdir):
>  *** 0341:            os.makedirs(outdir)
>      0342:        basename = self.d.getVar('IMAGE_BASENAME', True)
>      0343:        with open(os.path.join(outdir, basename) + '.env', 'w') as envf:
>      0344:            for var in self.d.getVar('WICVARS', True).split():
>      0345:                value = self.d.getVar(var, True)
> File: '/usr/lib/python2.7/os.py', lineno: 157, function: makedirs
>      0153:            if e.errno != errno.EEXIST:
>      0154:                raise
>      0155:        if tail == curdir:           # xxx/newdir/. exists if xxx/newdir exists
>      0156:            return
>  *** 0157:    mkdir(name, mode)
>      0158:
>      0159:def removedirs(name):
>      0160:    """removedirs(path)
>      0161:
> Exception: OSError: [Errno 17] File exists: '.../tmp-glibc/sysroots/cheetah/imgdata'
> 
> os.makedirs protects against racing on parent directories but not on the
> final part.
> 
> The sysroot directory will already exist so let's just try and make the
> imgdata directory and cope with the exception thrown if it already
> exists. This stops the race being fatal.
> 
> Once the directory has been created, there's no race on the actual file
> since the filename contains IMAGE_BASENAME.
> 
> Signed-off-by: Mike Crowe <mac at mcrowe.com>
> ---
>  meta/lib/oe/image.py | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/meta/lib/oe/image.py b/meta/lib/oe/image.py
> index b9eb3de..8c797ec 100644
> --- a/meta/lib/oe/image.py
> +++ b/meta/lib/oe/image.py
> @@ -1,5 +1,6 @@
>  from oe.utils import execute_pre_post_process
>  import os
> +import errno
>  import subprocess
>  import multiprocessing
>  
> @@ -337,8 +338,16 @@ class Image(ImageDepGraph):
>          """
>          stdir = self.d.getVar('STAGING_DIR_TARGET', True)
>          outdir = os.path.join(stdir, 'imgdata')
> -        if not os.path.exists(outdir):
> -            os.makedirs(outdir)
> +        try:
> +            # This may race against another image being created, so
> +            # let's just try and create the directory and just ignore
> +            # the error if it already exists. The parent directory
> +            # will already exist so there's no benefit to using
> +            # os.makedirs (which is also subject to the race.)
> +            os.mkdir(outdir)
> +        except OSError as e:
> +            if e.errno != errno.EEXIST:
> +                raise
>          basename = self.d.getVar('IMAGE_BASENAME', True)
>          with open(os.path.join(outdir, basename) + '.env', 'w') as envf:
>              for var in self.d.getVar('WICVARS', True).split():

How about using bb.utils.mkdirhier() which already does this?

Cheers,

Richard