New submission from Larry Hastings <la...@hastings.org>:
Serhiy Storchaka suggested (in private email, not on tracker or python-dev):
why not make follow_symlinks and effective_ids failover where possible?
Let's take the example of effective_ids first, that's simpler. Let's say the
user calls
os.access("x", os.F_OK, effective_ids=True)
But they doesn't have faccessat() for some reason. IF euid==uid, and
egid==gid, then it's harmless to ignore the effective_ids flag and just use
normal access().
Supporting this is easy: if effective_ids=True, and !defined(HAVE_FACCESSAT),
but we have all four of the get{e|}{u|g}id() functions, do the above comparison
and if it is just call access().
It's a bit more complicated with follow_symlinks. Let's say they call
os.chmod("x", 0o644, follow_symlinks=False)
As it happens, they're on Linux so they don't have lchmod() and their
fchmodat() doesn't support AT_SYMLINK_NOFOLLOW. But! "x" isn't a symbolic
link! In this case normal chmod would be fine fine.
How do we detect that the file is a symbolic link? That's easy, call lstat().
On Windows, if they gave us a wide path, call win32_lstat_w(). If they passed
in a non-default dir_fd, call fstatat() (if available).
The one place where we can't fail over gracefully: os.stat() If we don't have
the appropriate native stat function (lstat or fstatat), then obviously we
can't stat nofollow the file to see if it's not a symbolic link and call normal
stat(). Sad face.
The attached patch implements all of the above. It passes the regression test
suite on Linux 64-bit (with and without pydebug) and Windows 32-bit (Debug and
Release).
----------
assignee: larry
files: larry.kinder.gentler.follow_symlinks.1.diff
keywords: patch
messages: 163713
nosy: georg.brandl, larry, pitrou, storchaka
priority: normal
severity: normal
stage: patch review
status: open
title: Add failover for follow_symlinks and effective_ids where possible
type: behavior
Added file:
http://bugs.python.org/file26122/larry.kinder.gentler.follow_symlinks.1.diff
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