On 2021-01-06 02:44, Mark Geisert wrote:
Hi Noel,
Noel Grandin via Cygwin wrote:
Hi
Does the cygwin
tempfile()
API use the Win32
FILE_ATTRIBUTE_TEMPORARY
flag on the files it creates?
Asking because that makes a fairly significant performance difference when
creating very short lived temp files.
Good question! If one specifies O_TMPFILE as one of the flags on an open()
call, Cygwin does set that Win32 attribute as desired. Unfortunately, Cygwin's
tmpfile() is supplied by newlib and it does not specify O_TMPFILE on its
underlying open() call.
That looks like a bug to me, unless I'm missing something subtle there; I'll
submit a patch and find out.
O_TMPFILE is only implemented under winsup/cygwin, and only defined for newlib
under Cygwin:
https://sourceware.org/git/?p=newlib-cygwin.git;a=blob;f=newlib/libc/include/sys/_default_fcntl.h
see:
https://sourceware.org/git/?p=newlib-cygwin.git;a=commitdiff;h=0aa99373c1d01b19a7f8ba53e8c7749358480f3e
https://cygwin.com/pipermail/cygwin/2018-February/236018.html
and:
https://cygwin.com/pipermail/cygwin/2018-February/235869.html
https://sourceware.org/git/?p=newlib-cygwin.git;a=commitdiff;h=7ae73be14194ccadc9a7557be33c3940ca4667cb
You should allow linkat to reverse the applied attributes to make the file
permanent, which may be taken care of in the patch above to
fhandler_disk_file::link;
from Linux open(2) see
https://man7.org/linux/man-pages/man2/open.2.html:
"O_TMPFILE must be specified with one of O_RDWR or O_WRONLY and,
optionally, O_EXCL. If O_EXCL is not specified, then linkat(2) can be
used to link the temporary file into the filesystem, making it
permanent, using code like the following:
char path[PATH_MAX];
fd = open("/path/to/dir", O_TMPFILE | O_RDWR, S_IRUSR | S_IWUSR);
/* File I/O on 'fd'... */
snprintf(path, PATH_MAX, "/proc/self/fd/%d", fd);
linkat(AT_FDCWD, path, AT_FDCWD, "/path/for/file",
AT_SYMLINK_FOLLOW);
"
although the implementation may not currently handle O_EXCL.
--
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada
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