On Windows, freopen reopened a stream through _wfreopen, which opens the file without FILE_SHARE_DELETE, so remove or rename of the file failed while the stream was open, unlike fopen streams and POSIX unlink/rename of an open file. freopen now closes the previous stream and opens the new file through the same CreateFileW path fopen uses, so the reopened stream shares delete access. Host standard streams and an empty filename keep the _wfreopen path. Reference: FreeBSD 11 unlink(2) and rename(2) succeed on a file that is open.
On Windows the UCRT does not switch an r+, w+ or a+ stream from writing
to reading without fflush or fseek: fread after fwrite returned bytes of
the write buffer and the next flush wrote them over the file, and ungetc
failed on an update stream that was not already reading. On Linux glibc
does not switch either for ungetc, which pushes the byte back over the
pending write, drops the write and can corrupt the heap on the next read,
or for an fread of at least the buffer size, which drops the write and
reads from the old offset.
fread, fgetc, getc_unlocked, fgets, ungetc, ungetwc and fscanf now flush
pending output and mark the stream as reading first, as FreeBSD 11.4's
__srefill and __ungetc do, through _IO_switch_to_get_mode on glibc.
Writes directly after reads still go through the UCRT on Windows; the
gap is recorded in the libc technical debt.
fflush threw when the host flush failed, which ends the title on an
ordinary write error such as a full disk. FreeBSD's __sflush sets the
stream's error flag and returns EOF, as C17 7.21.5.2 asks. fflush now
returns the host result and keeps the guest stream's error flag in sync,
as fwrite, fputs and fclose already do since #4380 and #3926.
fopen opened its stream with _wfopen, which shares read and write
access but not delete access. While the guest held a stream open,
rename of its file failed with EIO and remove with EBUSY. POSIX rename
and remove work on open files, as on Linux and FreeBSD, and since
#3677 the descriptors sceKernelOpen returns share delete access.
fopen now creates the handle with CreateFileW sharing read, write and
delete, with the access and creation disposition of the mode, and
wraps it with _open_osfhandle and _wfdopen, keeping append mode. A
failed CreateFileW sets errno through the error mapping #3677 added to
libkernel's NativeOpen, which moves to libc as
WindowsOpenError_nid_no_patch so that both use it. freopen still
reopens through _wfreopen; TechnicalDebt records it.
Dean