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Support symbolic links on Windows #2018

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Support symbolic links on Windows #2018

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6ec4ff7
mingw: don't call `GetFileAttributes()` twice in `mingw_lstat()`
kblees May 12, 2015
5d83a8a
mingw: implement `stat()` with symlink support
kblees May 15, 2015
d3953f1
mingw: drop the separate `do_lstat()` function
kblees May 11, 2015
a635578
mingw: let `mingw_lstat()` error early upon problems with reparse points
kblees May 23, 2015
8b7f5a8
mingw: teach dirent about symlinks
kblees Jan 10, 2017
1159e86
mingw: compute the correct size for symlinks in `mingw_lstat()`
billziss-gh May 28, 2020
4aeccd6
mingw: factor out the retry logic
kblees May 19, 2015
86c0742
mingw: change default of `core.symlinks` to false
kblees May 23, 2015
9a0093d
mingw: add symlink-specific error codes
kblees May 15, 2015
5dc90f9
mingw: handle symlinks to directories in `mingw_unlink()`
kblees May 23, 2015
3670a0a
mingw: support renaming symlinks
kblees May 19, 2015
f79cf31
mingw: allow `mingw_chdir()` to change to symlink-resolved directories
kblees May 23, 2015
1ae9c63
mingw: implement `readlink()`
kblees May 23, 2015
4e0ac43
mingw: implement basic `symlink()` functionality (file symlinks only)
kblees May 23, 2015
3d479fd
mingw: add support for symlinks to directories
kblees May 23, 2015
fb6aa46
mingw: try to create symlinks without elevated permissions
dscho May 30, 2017
40c3f7f
mingw: emulate `stat()` a little more faithfully
dscho Mar 2, 2020
afcf2bb
mingw: special-case index entries for symlinks with buggy size
dscho Jun 4, 2020
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6 changes: 2 additions & 4 deletions compat/mingw-posix.h
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Original file line number Diff line number Diff line change
Expand Up @@ -121,10 +121,6 @@ struct utsname {
* trivial stubs
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@gitgitgadget gitgitgadget bot Dec 18, 2025

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On the Git mailing list, Johannes Sixt wrote (reply to this):

Am 17.12.25 um 15:08 schrieb Karsten Blees via GitGitGadget:
> From: Karsten Blees <blees@dcon.de>
> 
> Implement `readlink()` by reading NTFS reparse points via the
> `read_reparse_point()` function that was introduced earlier to determine
> the length of symlink targets. Works for symlinks and directory
> junctions. If symlinks are disabled, fail with `ENOSYS`.

This last sentence is obsolete, I think, because I cannot see how the
patch achieves a failure with ENOSYS.

> 
> Signed-off-by: Karsten Blees <blees@dcon.de>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  compat/mingw-posix.h |  3 +--
>  compat/mingw.c       | 24 ++++++++++++++++++++++++
>  2 files changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/compat/mingw-posix.h b/compat/mingw-posix.h
> index 0939feff27..896aa976b1 100644
> --- a/compat/mingw-posix.h
> +++ b/compat/mingw-posix.h
> @@ -121,8 +121,6 @@ struct utsname {
>   * trivial stubs
>   */
>  
> -static inline int readlink(const char *path UNUSED, char *buf UNUSED, size_t bufsiz UNUSED)
> -{ errno = ENOSYS; return -1; }
>  static inline int symlink(const char *oldpath UNUSED, const char *newpath UNUSED)
>  { errno = ENOSYS; return -1; }
>  static inline int fchmod(int fildes UNUSED, mode_t mode UNUSED)
> @@ -197,6 +195,7 @@ int setitimer(int type, struct itimerval *in, struct itimerval *out);
>  int sigaction(int sig, struct sigaction *in, struct sigaction *out);
>  int link(const char *oldpath, const char *newpath);
>  int uname(struct utsname *buf);
> +int readlink(const char *path, char *buf, size_t bufsiz);
>  
>  /*
>   * replacements of existing functions
> diff --git a/compat/mingw.c b/compat/mingw.c
> index 5d2a8c247c..b407a2ac07 100644
> --- a/compat/mingw.c
> +++ b/compat/mingw.c
> @@ -2698,6 +2698,30 @@ int link(const char *oldpath, const char *newpath)
>  	return 0;
>  }
>  
> +int readlink(const char *path, char *buf, size_t bufsiz)
> +{
> +	WCHAR wpath[MAX_PATH];
> +	char tmpbuf[MAX_PATH];
> +	int len;
> +	DWORD tag;
> +
> +	if (xutftowcs_path(wpath, path) < 0)
> +		return -1;
> +
> +	if (read_reparse_point(wpath, TRUE, tmpbuf, &len, &tag) < 0)
> +		return -1;
> +
> +	/*
> +	 * Adapt to strange readlink() API: Copy up to bufsiz *bytes*, potentially
> +	 * cutting off a UTF-8 sequence. Insufficient bufsize is *not* a failure
> +	 * condition. There is no conversion function that produces invalid UTF-8,
> +	 * so convert to a (hopefully large enough) temporary buffer, then memcpy
> +	 * the requested number of bytes (including '\0' for robustness).
> +	 */
> +	memcpy(buf, tmpbuf, min(bufsiz, len + 1));
> +	return min(bufsiz, len);
> +}
> +
>  pid_t waitpid(pid_t pid, int *status, int options)
>  {
>  	HANDLE h = OpenProcess(SYNCHRONIZE | PROCESS_QUERY_INFORMATION,

-- Hannes

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@gitgitgadget gitgitgadget bot Jan 9, 2026

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Johannes Schindelin wrote on the Git mailing list (how to reply to this email):

Hi Hannes,

On Thu, 18 Dec 2025, Johannes Sixt wrote:

> Am 17.12.25 um 15:08 schrieb Karsten Blees via GitGitGadget:
> > From: Karsten Blees <blees@dcon.de>
> > 
> > Implement `readlink()` by reading NTFS reparse points via the
> > `read_reparse_point()` function that was introduced earlier to determine
> > the length of symlink targets. Works for symlinks and directory
> > junctions. If symlinks are disabled, fail with `ENOSYS`.
> 
> This last sentence is obsolete, I think, because I cannot see how the
> patch achieves a failure with ENOSYS.

Indeed, this is obsolete. Just like with the ELOOP commit message comment
of 02/18, I must have dropped this because reading symlinks should work
even if creating symlinks has been disabled via `core.symlinks`. Here is
the range-diff between the last version of the patch that still had the
ENOSYS logic and the first version that lacked it (Git for Windows-only
commits):

1:  4f353d988de4 ! 1:  1d079621427c Win32: implement readlink()

   @@ compat/mingw.c: int link(const char *oldpath, const char *newpath)
    +	char tmpbuf[MAX_LONG_PATH];
    +	int len;
    +
   -+	/* fail if symlinks are disabled */
   -+	if (!has_symlinks) {
   -+		errno = ENOSYS;
   -+		return -1;
   -+	}
   -+
    +	if (xutftowcs_long_path(wpath, path) < 0)
    +		return -1;
    +

So: Unfortunately I have no record that I can readily produce that would
motivate that change. Given that it happened during the same v2.19.2
timeframe as the ELOOP change, there must have been some broader
discussion about this, but I could not find it, not even in the release
notes of that version:
https://github.com/git-for-windows/git/releases/tag/v2.19.2.windows.1

All I can present is the reconstructed rationale that just because Git is
not allowed (or able) to create symlinks does not mean that they cannot
exist, and therefore Git should at least read and parse them as expected,
independent of the value of `core.symlinks`.

So yes, this part of the commit message is just simply confusing at this
point, so I'll drop it.

Ciao,
Johannes

*/

static inline int readlink(const char *path UNUSED, char *buf UNUSED, size_t bufsiz UNUSED)
{ errno = ENOSYS; return -1; }
static inline int symlink(const char *oldpath UNUSED, const char *newpath UNUSED)
{ errno = ENOSYS; return -1; }
static inline int fchmod(int fildes UNUSED, mode_t mode UNUSED)
{ errno = ENOSYS; return -1; }
#ifndef __MINGW64_VERSION_MAJOR
Expand Down Expand Up @@ -197,6 +193,8 @@ int setitimer(int type, struct itimerval *in, struct itimerval *out);
int sigaction(int sig, struct sigaction *in, struct sigaction *out);
int link(const char *oldpath, const char *newpath);
int uname(struct utsname *buf);
int symlink(const char *target, const char *link);
int readlink(const char *path, char *buf, size_t bufsiz);

/*
* replacements of existing functions
Expand Down
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