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mingw: fix mingw_open_append to work with named pipes

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Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Acked-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff Hostetler
2018-09-11 13:06:02 -07:00
committed by Junio C Hamano
parent 06ba9d03e3
commit eeaf7ddac7
2 changed files with 34 additions and 4 deletions
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36
compat/mingw.c
View File

@ -341,6 +341,19 @@ int mingw_mkdir(const char *path, int mode)
return ret;
}
/*
* Calling CreateFile() using FILE_APPEND_DATA and without FILE_WRITE_DATA
* is documented in [1] as opening a writable file handle in append mode.
* (It is believed that) this is atomic since it is maintained by the
* kernel unlike the O_APPEND flag which is racily maintained by the CRT.
*
* [1] https://docs.microsoft.com/en-us/windows/desktop/fileio/file-access-rights-constants
*
* This trick does not appear to work for named pipes. Instead it creates
* a named pipe client handle that cannot be written to. Callers should
* just use the regular _wopen() for them. (And since client handle gets
* bound to a unique server handle, it isn't really an issue.)
*/
static int mingw_open_append(wchar_t const *wfilename, int oflags, ...)
{
HANDLE handle;
@ -360,10 +373,12 @@ static int mingw_open_append(wchar_t const *wfilename, int oflags, ...)
NULL, create, FILE_ATTRIBUTE_NORMAL, NULL);
if (handle == INVALID_HANDLE_VALUE)
return errno = err_win_to_posix(GetLastError()), -1;
/*
* No O_APPEND here, because the CRT uses it only to reset the
* file pointer to EOF on write(); but that is not necessary
* for a file created with FILE_APPEND_DATA.
* file pointer to EOF before each write(); but that is not
* necessary (and may lead to races) for a file created with
* FILE_APPEND_DATA.
*/
fd = _open_osfhandle((intptr_t)handle, O_BINARY);
if (fd < 0)
@ -371,6 +386,21 @@ static int mingw_open_append(wchar_t const *wfilename, int oflags, ...)
return fd;
}
/*
* Does the pathname map to the local named pipe filesystem?
* That is, does it have a "//./pipe/" prefix?
*/
static int is_local_named_pipe_path(const char *filename)
{
return (is_dir_sep(filename[0]) &&
is_dir_sep(filename[1]) &&
filename[2] == '.' &&
is_dir_sep(filename[3]) &&
!strncasecmp(filename+4, "pipe", 4) &&
is_dir_sep(filename[8]) &&
filename[9]);
}
int mingw_open (const char *filename, int oflags, ...)
{
typedef int (*open_fn_t)(wchar_t const *wfilename, int oflags, ...);
@ -387,7 +417,7 @@ int mingw_open (const char *filename, int oflags, ...)
if (filename && !strcmp(filename, "/dev/null"))
filename = "nul";
if (oflags & O_APPEND)
if ((oflags & O_APPEND) && !is_local_named_pipe_path(filename))
open_fn = mingw_open_append;
else
open_fn = _wopen;

2
t/t0051-windows-named-pipe.sh
View File

@ -4,7 +4,7 @@ test_description='Windows named pipes'
. ./test-lib.sh
test_expect_failure MINGW 'o_append write to named pipe' '
test_expect_success MINGW 'o_append write to named pipe' '
GIT_TRACE="$(pwd)/expect" git status >/dev/null 2>&1 &&
{ test-tool windows-named-pipe t0051 >actual 2>&1 & } &&
pid=$! &&