Fix issue with Link.target and Link.targetSync failing on some file systems

Fix issue with Link.target and Link.targetSync failing on some file systems

Don't rely on information from lstat64 for the size of the link target. Get
the actual length from just reading the link target.

BUG=http://dartbug.com/21987
R=kustermann@google.com

Committed: https://code.google.com/p/dart/source/detail?r=43066

[kustermann, 2015-01-22 09:00:19]

lgtm

https://codereview.chromium.org/860343002/diff/1/runtime/bin/file_linux.cc
File runtime/bin/file_linux.cc (left):

https://codereview.chromium.org/860343002/diff/1/runtime/bin/file_linux.cc#ol...
runtime/bin/file_linux.cc:371: size_t target_size = link_stats.st_size;
One alternative would be to check if "target_size > 0" and if so, trust it,
otherwise fallback to a 1024 buffer.

https://codereview.chromium.org/860343002/diff/1/runtime/bin/file_linux.cc
File runtime/bin/file_linux.cc (right):

https://codereview.chromium.org/860343002/diff/1/runtime/bin/file_linux.cc#ne...
runtime/bin/file_linux.cc:374: const int kBufferSize = 1024;
You could consider using PATH_MAX here.

https://codereview.chromium.org/860343002/diff/1/tests/standalone/io/regress_...
File tests/standalone/io/regress_21987_test.dart (right):

https://codereview.chromium.org/860343002/diff/1/tests/standalone/io/regress_...
tests/standalone/io/regress_21987_test.dart:17: asyncEnd();
You could assert that it is 'Platform.executable', right?

[Søren Gjesse, 2015-01-22 10:25:52]

https://codereview.chromium.org/860343002/diff/1/runtime/bin/file_linux.cc
File runtime/bin/file_linux.cc (left):

https://codereview.chromium.org/860343002/diff/1/runtime/bin/file_linux.cc#ol...
runtime/bin/file_linux.cc:371: size_t target_size = link_stats.st_size;
On 2015/01/22 09:00:19, kustermann wrote:
> One alternative would be to check if "target_size > 0" and if so, trust it,
> otherwise fallback to a 1024 buffer.

I thought about that, but then (unlikely) the link could have changed between
this and the readlink call, so I decided to stay safe.

https://codereview.chromium.org/860343002/diff/1/runtime/bin/file_linux.cc
File runtime/bin/file_linux.cc (right):

https://codereview.chromium.org/860343002/diff/1/runtime/bin/file_linux.cc#ne...
runtime/bin/file_linux.cc:374: const int kBufferSize = 1024;
On 2015/01/22 09:00:19, kustermann wrote:
> You could consider using PATH_MAX here.

Done.

https://codereview.chromium.org/860343002/diff/1/tests/standalone/io/regress_...
File tests/standalone/io/regress_21987_test.dart (right):

https://codereview.chromium.org/860343002/diff/1/tests/standalone/io/regress_...
tests/standalone/io/regress_21987_test.dart:17: asyncEnd();
On 2015/01/22 09:00:19, kustermann wrote:
> You could assert that it is 'Platform.executable', right?

No that is not possible, as 'Platform.executable' is whatever is passed on the
command line (e.g. out/DebugIA32/dart), and /proc/self/exe is the resolved
absolute path.

[Søren Gjesse, 2015-01-22 10:27:17]

Committed patchset #2 (id:20001) manually as 43066 (presubmit successful).