[PATCH] Cygwin: Have tmpfile(3) use O_TMPFILE
Wed Feb 10 09:07:30 GMT 2021
Corinna Vinschen via Cygwin-patches wrote:
> Hi Mark,
> On Feb 9 02:50, Mark Geisert wrote:
>> Per discussion on cygwin-developers, a Cygwin tmpfile(3) implementation
>> has been added to syscalls.cc. This overrides the one supplied by
>> newlib. Then the open(2) flag O_TMPFILE was added to the open call that
>> tmpfile internally makes.
>> winsup/cygwin/release/3.2.0 | 4 ++++
>> winsup/cygwin/syscalls.cc | 20 ++++++++++++++++++++
>> 2 files changed, 24 insertions(+)
>> diff --git a/winsup/cygwin/release/3.2.0 b/winsup/cygwin/release/3.2.0
>> index f748a9bc8..d02d16863 100644
>> --- a/winsup/cygwin/release/3.2.0
>> +++ b/winsup/cygwin/release/3.2.0
>> @@ -19,6 +19,10 @@ What changed:
>> - A few FAQ updates.
>> +- Have tmpfile(3) make use of Win32 FILE_ATTRIBUTE_TEMPORARY via open(2)
>> + flag O_TMPFILE.
>> + Addresses: https://cygwin.com/pipermail/cygwin/2021-January/247304.html
>> Bug Fixes
>> diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
>> index 52a020f07..b79c1c7cd 100644
>> --- a/winsup/cygwin/syscalls.cc
>> +++ b/winsup/cygwin/syscalls.cc
>> @@ -5225,3 +5225,23 @@ pipe2 (int filedes, int mode)
>> syscall_printf ("%R = pipe2([%d, %d], %y)", res, read, write, mode);
>> return res;
>> +extern "C" FILE *
>> +tmpfile (void)
>> + char *dir = getenv ("TMPDIR");
> This isn't what Linux tmpfile does. Per the man page, it tries to
> create the file in P_tmpdir first, and if that fails, it tries
Oops, I was following newlib's code here. I'll adjust this.
>> + if (!dir)
>> + dir = P_tmpdir;
>> + int fd = open (dir, O_RDWR | O_CREAT | O_BINARY | O_TMPFILE,
> You have to specify O_EXCL here. The idea is that this file cannot be
> made permanent, and missing the O_EXCL flag allows exactly that. See
> https://man7.org/linux/man-pages/man2/open.2.html, the lengthy
> description in terms of O_TMPFILE.
I started out with O_EXCL as you suggested, but found syscalls.cc:1504 reporting
EEXIST. Is there some clash there between fh->exists() and O_TMPFILE? Hmm.
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