[morty][PATCH] fetch2: Do not fail to create symbolic links if they already exist

[morty][PATCH] fetch2: Do not fail to create symbolic links if they already exist

[Peter Kjellerstedt]

From: Peter Kjellerstedt <peter.kjellerstedt@axis.com>

When the fetcher retrieves file:// URLs, there is no lock file being
used. This means that in case two separate tasks (typically from two
concurrent invocations of bitbake) want to download the same file://
URL at the same time, there is a very small chance that they also end
up wanting to create a symbolic link to the file at the same time.
This would previously lead to one of the tasks failing as the other
task would have created the link.

Signed-off-by: Peter Kjellerstedt <pkj@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
---

This is a backport of 58a03531c8183b165bb7dcad86d8559c92bc150d on
master.

 bitbake/lib/bb/fetch2/__init__.py | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/bitbake/lib/bb/fetch2/__init__.py b/bitbake/lib/bb/fetch2/__init__.py
index cd7362c44a..f36f01a707 100644
--- a/bitbake/lib/bb/fetch2/__init__.py
+++ b/bitbake/lib/bb/fetch2/__init__.py
@@ -967,7 +967,14 @@ def try_mirror_url(fetch, origud, ud, ld, check = False):
                 open(ud.donestamp, 'w').close()
             dest = os.path.join(dldir, os.path.basename(ud.localpath))
             if not os.path.exists(dest):
-                os.symlink(ud.localpath, dest)
+                # In case this is executing without any file locks held (as is
+                # the case for file:// URLs), two tasks may end up here at the
+                # same time, in which case we do not want the second task to
+                # fail when the link has already been created by the first task.
+                try:
+                    os.symlink(ud.localpath, dest)
+                except FileExistsError:
+                    pass
             if not verify_donestamp(origud, ld) or origud.method.need_update(origud, ld):
                 origud.method.download(origud, ld)
                 if hasattr(origud.method,"build_mirror_data"):
@@ -979,7 +986,11 @@ def try_mirror_url(fetch, origud, ud, ld, check = False):
                 # Broken symbolic link
                 os.unlink(origud.localpath)
 
-            os.symlink(ud.localpath, origud.localpath)
+            # As per above, in case two tasks end up here simultaneously.
+            try:
+                os.symlink(ud.localpath, origud.localpath)
+            except FileExistsError:
+                pass
         update_stamp(origud, ld)
         return ud.localpath
 
-- 
2.12.0

Re: [morty][PATCH] fetch2: Do not fail to create symbolic links if they already exist

[akuster808]

On 04/03/2017 05:59 AM, Peter Kjellerstedt wrote:
> From: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
>
> When the fetcher retrieves file:// URLs, there is no lock file being
> used. This means that in case two separate tasks (typically from two
> concurrent invocations of bitbake) want to download the same file://
> URL at the same time, there is a very small chance that they also end
> up wanting to create a symbolic link to the file at the same time.
> This would previously lead to one of the tasks failing as the other
> task would have created the link.
>
> Signed-off-by: Peter Kjellerstedt <pkj@axis.com>
> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

thanks, I am the process of stagging changes.
-armin
> ---
>
> This is a backport of 58a03531c8183b165bb7dcad86d8559c92bc150d on
> master.
>
>   bitbake/lib/bb/fetch2/__init__.py | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/bitbake/lib/bb/fetch2/__init__.py b/bitbake/lib/bb/fetch2/__init__.py
> index cd7362c44a..f36f01a707 100644
> --- a/bitbake/lib/bb/fetch2/__init__.py
> +++ b/bitbake/lib/bb/fetch2/__init__.py
> @@ -967,7 +967,14 @@ def try_mirror_url(fetch, origud, ud, ld, check = False):
>                   open(ud.donestamp, 'w').close()
>               dest = os.path.join(dldir, os.path.basename(ud.localpath))
>               if not os.path.exists(dest):
> -                os.symlink(ud.localpath, dest)
> +                # In case this is executing without any file locks held (as is
> +                # the case for file:// URLs), two tasks may end up here at the
> +                # same time, in which case we do not want the second task to
> +                # fail when the link has already been created by the first task.
> +                try:
> +                    os.symlink(ud.localpath, dest)
> +                except FileExistsError:
> +                    pass
>               if not verify_donestamp(origud, ld) or origud.method.need_update(origud, ld):
>                   origud.method.download(origud, ld)
>                   if hasattr(origud.method,"build_mirror_data"):
> @@ -979,7 +986,11 @@ def try_mirror_url(fetch, origud, ud, ld, check = False):
>                   # Broken symbolic link
>                   os.unlink(origud.localpath)
>   
> -            os.symlink(ud.localpath, origud.localpath)
> +            # As per above, in case two tasks end up here simultaneously.
> +            try:
> +                os.symlink(ud.localpath, origud.localpath)
> +            except FileExistsError:
> +                pass
>           update_stamp(origud, ld)
>           return ud.localpath
>