Re: [PATCH] lib/oe/path: try hardlinking instead of guessing when it might fail

[Henning Schild <henning.schild@siemens.com>]

This is related to fixing an issue with "--exclude-path" in wic. On the
Isar side i have everything in place and might send it. But we need
that upstream fix ... or some workaround if that does not get merged.

Henning

On Fri, 24 Jan 2020 14:48:47 +0100
Henning Schild <henning.schild@siemens.com> wrote:

> From: Henning Schild <henning.schild@siemens.com>
> 
> The comparison of the stat st_dev is not enough to judge whether
> hardlinking will work. One example would be where you try and hardlink
> across two bind-mounts of a directory. The st_dev will be the same and
> the operation will still fail.
> 
> Instead of implementing a check to try and figure out hardlink support
> just try hardlinking and fall back to a copy when running into an
> exception.
> 
> Signed-off-by: Henning Schild <henning.schild@siemens.com>
> ---
>  meta/lib/oe/path.py | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/meta/lib/oe/path.py b/meta/lib/oe/path.py
> index fa209b9795..082972457b 100644
> --- a/meta/lib/oe/path.py
> +++ b/meta/lib/oe/path.py
> @@ -99,7 +99,22 @@ def copyhardlinktree(src, dst):
>      if os.path.isdir(src) and not len(os.listdir(src)):
>          return
>  
> -    if (os.stat(src).st_dev ==  os.stat(dst).st_dev):
> +    canhard = False
> +    testfile = None
> +    for root, dirs, files in os.walk(src):
> +        if len(files):
> +            testfile = os.path.join(root, files[0])
> +            break
> +
> +    if testfile is not None:
> +        try:
> +            os.link(testfile, os.path.join(dst, 'testfile'))
> +            os.unlink(os.path.join(dst, 'testfile'))
> +            canhard = True
> +        except Exception as e:
> +            bb.debug(2, "Hardlink test failed with " + str(e))
> +
> +    if (canhard):
>          # Need to copy directories only with tar first since cp will
> error if two # writers try and create a directory at the same time
>          cmd = "cd %s; find . -type d -print | tar --xattrs
> --xattrs-include='*' -cf - -S -C %s -p --no-recursion --files-from -
> | tar --xattrs --xattrs-include='*' -xhf - -C %s" % (src, src, dst)
> @@ -121,12 +136,9 @@ def copyhardlinktree(src, dst): def
> copyhardlink(src, dst): """Make a hard link when possible, otherwise
> copy.""" 
> -    # We need to stat the destination directory as the destination
> file probably
> -    # doesn't exist yet.
> -    dstdir = os.path.dirname(dst)
> -    if os.stat(src).st_dev == os.stat(dstdir).st_dev:
> +    try:
>          os.link(src, dst)
> -    else:
> +    except OSError:
>          shutil.copy(src, dst)
>  
>  def remove(path, recurse=True):