From: Jeff Hostetler <git@jeffhostetler.com>
To: Johannes Sixt <j6t@kdbg.org>, jeffhost@microsoft.com
Cc: Jeff Hostetler via GitGitGadget <gitgitgadget@gmail.com>,
git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH v2 2/2] mingw: fix mingw_open_append to work with named pipes
Date: Mon, 10 Sep 2018 16:07:27 -0400 [thread overview]
Message-ID: <eedde82a-dedb-88ba-4bb9-fbcfdd7f1b62@jeffhostetler.com> (raw)
In-Reply-To: <a309396f-bb33-477d-5d92-a98699f5a856@kdbg.org>
On 9/10/2018 3:45 PM, Johannes Sixt wrote:
> Am 10.09.18 um 19:05 schrieb Jeff Hostetler via GitGitGadget:
>> diff --git a/compat/mingw.c b/compat/mingw.c
>> index 858ca14a57..f87376b26a 100644
>> --- a/compat/mingw.c
>> +++ b/compat/mingw.c
>> @@ -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 +386,23 @@ static int mingw_open_append(wchar_t const
>> *wfilename, int oflags, ...)
>> return fd;
>> }
>> +#define IS_SBS(ch) (((ch) == '/') || ((ch) == '\\'))
>> +/*
>> + * Does the pathname map to the local named pipe filesystem?
>> + * That is, does it have a "//./pipe/" prefix?
>> + */
>> +static int mingw_is_local_named_pipe_path(const char *filename)
>> +{
>> + return (IS_SBS(filename[0]) &&
>> + IS_SBS(filename[1]) &&
>> + filename[2] == '.' &&
>> + IS_SBS(filename[3]) &&
>> + !strncasecmp(filename+4, "pipe", 4) &&
>> + IS_SBS(filename[8]) &&
>> + filename[9]);
>> +}
>> +#undef IS_SBS
>> +
>> int mingw_open (const char *filename, int oflags, ...)
>> {
>> typedef int (*open_fn_t)(wchar_t const *wfilename, int oflags,
>> ...);
>> @@ -387,7 +419,7 @@ int mingw_open (const char *filename, int oflags,
>> ...)
>> if (filename && !strcmp(filename, "/dev/null"))
>> filename = "nul";
>> - if (oflags & O_APPEND)
>> + if ((oflags & O_APPEND) &&
>> !mingw_is_local_named_pipe_path(filename))
>> open_fn = mingw_open_append;
>> else
>> open_fn = _wopen;
>
> This looks reasonable.
Thanks for the review.
>
> I wonder which part of the code uses local named pipes. Is it downstream
> in Git for Windows or one of the topics in flight?
>
> -- Hannes
I'm wanting to use them as a tracing target option in my trace2 series
currently in progress.
Jeff
next prev parent reply other threads:[~2018-09-10 20:07 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-07 18:19 [PATCH 0/2] Fixup for js/mingw-o-append Jeff Hostetler via GitGitGadget
2018-09-07 18:19 ` [PATCH 1/2] t0051: test GIT_TRACE to a windows named pipe Jeff Hostetler via GitGitGadget
2018-09-09 7:28 ` Sebastian Schuberth
2018-09-10 13:21 ` Jeff Hostetler
2018-09-07 18:19 ` [PATCH 2/2] mingw: fix mingw_open_append to work with named pipes Jeff Hostetler via GitGitGadget
2018-09-08 9:26 ` Johannes Sixt
2018-09-08 18:31 ` Johannes Sixt
2018-09-10 15:44 ` Jeff Hostetler
2018-09-10 16:42 ` Junio C Hamano
2018-09-10 16:55 ` Jeff Hostetler
2018-09-07 18:36 ` [PATCH 0/2] Fixup for js/mingw-o-append Jeff Hostetler
2018-09-10 17:05 ` [PATCH v2 " Jeff Hostetler via GitGitGadget
2018-09-10 17:05 ` [PATCH v2 1/2] t0051: test GIT_TRACE to a windows named pipe Jeff Hostetler via GitGitGadget
2018-09-10 17:05 ` [PATCH v2 2/2] mingw: fix mingw_open_append to work with named pipes Jeff Hostetler via GitGitGadget
2018-09-10 19:45 ` Johannes Sixt
2018-09-10 20:07 ` Jeff Hostetler [this message]
2018-09-10 22:00 ` Junio C Hamano
2018-09-11 14:25 ` Jeff Hostetler
2018-09-11 20:05 ` [PATCH v3 0/2] Fixup for js/mingw-o-append Jeff Hostetler via GitGitGadget
2018-09-11 20:06 ` [PATCH v3 1/2] t0051: test GIT_TRACE to a windows named pipe Jeff Hostetler via GitGitGadget
2018-09-11 20:06 ` [PATCH v3 2/2] mingw: fix mingw_open_append to work with named pipes Jeff Hostetler via GitGitGadget
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