From: "Karsten Blees via GitGitGadget" <gitgitgadget@gmail•com>
To: git@vger•kernel.org
Cc: Ben Knoble <ben.knoble@gmail•com>, Johannes Sixt <j6t@kdbg•org>,
Karsten Blees <karsten.blees@gmail•com>,
Johannes Schindelin <johannes.schindelin@gmx•de>,
Karsten Blees <karsten.blees@gmail•com>
Subject: [PATCH v2 15/18] mingw: add support for symlinks to directories
Date: Fri, 09 Jan 2026 20:05:12 +0000 [thread overview]
Message-ID: <3d479fd47e68242b028e1bbfd0019dfb0ededac8.1767989115.git.gitgitgadget@gmail.com> (raw)
In-Reply-To: <pull.2018.v2.git.1767989115.gitgitgadget@gmail.com>
From: Karsten Blees <karsten.blees@gmail•com>
Symlinks on Windows have a flag that indicates whether the target is a
file or a directory. Symlinks of wrong type simply don't work. This even
affects core Win32 APIs (e.g. `DeleteFile()` refuses to delete directory
symlinks).
However, `CreateFile()` with FILE_FLAG_BACKUP_SEMANTICS does work. Check
the target type by first creating a tentative file symlink, opening it,
and checking the type of the resulting handle. If it is a directory,
recreate the symlink with the directory flag set.
It is possible to create symlinks before the target exists (or in case
of symlinks to symlinks: before the target type is known). If this
happens, create a tentative file symlink and postpone the directory
decision: keep a list of phantom symlinks to be processed whenever a new
directory is created in `mingw_mkdir()`.
Limitations: This algorithm may fail if a link target changes from file
to directory or vice versa, or if the target directory is created in
another process. It's the best Git can do, though.
Signed-off-by: Karsten Blees <karsten.blees@gmail•com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx•de>
---
compat/mingw.c | 164 +++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 164 insertions(+)
diff --git a/compat/mingw.c b/compat/mingw.c
index 8d366794c4..59a32e454e 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -296,6 +296,131 @@ int mingw_core_config(const char *var, const char *value,
return 0;
}
+static inline int is_wdir_sep(wchar_t wchar)
+{
+ return wchar == L'/' || wchar == L'\\';
+}
+
+static const wchar_t *make_relative_to(const wchar_t *path,
+ const wchar_t *relative_to, wchar_t *out,
+ size_t size)
+{
+ size_t i = wcslen(relative_to), len;
+
+ /* Is `path` already absolute? */
+ if (is_wdir_sep(path[0]) ||
+ (iswalpha(path[0]) && path[1] == L':' && is_wdir_sep(path[2])))
+ return path;
+
+ while (i > 0 && !is_wdir_sep(relative_to[i - 1]))
+ i--;
+
+ /* Is `relative_to` in the current directory? */
+ if (!i)
+ return path;
+
+ len = wcslen(path);
+ if (i + len + 1 > size) {
+ error("Could not make '%ls' relative to '%ls' (too large)",
+ path, relative_to);
+ return NULL;
+ }
+
+ memcpy(out, relative_to, i * sizeof(wchar_t));
+ wcscpy(out + i, path);
+ return out;
+}
+
+enum phantom_symlink_result {
+ PHANTOM_SYMLINK_RETRY,
+ PHANTOM_SYMLINK_DONE,
+ PHANTOM_SYMLINK_DIRECTORY
+};
+
+/*
+ * Changes a file symlink to a directory symlink if the target exists and is a
+ * directory.
+ */
+static enum phantom_symlink_result
+process_phantom_symlink(const wchar_t *wtarget, const wchar_t *wlink)
+{
+ HANDLE hnd;
+ BY_HANDLE_FILE_INFORMATION fdata;
+ wchar_t relative[MAX_PATH];
+ const wchar_t *rel;
+
+ /* check that wlink is still a file symlink */
+ if ((GetFileAttributesW(wlink)
+ & (FILE_ATTRIBUTE_REPARSE_POINT | FILE_ATTRIBUTE_DIRECTORY))
+ != FILE_ATTRIBUTE_REPARSE_POINT)
+ return PHANTOM_SYMLINK_DONE;
+
+ /* make it relative, if necessary */
+ rel = make_relative_to(wtarget, wlink, relative, ARRAY_SIZE(relative));
+ if (!rel)
+ return PHANTOM_SYMLINK_DONE;
+
+ /* let Windows resolve the link by opening it */
+ hnd = CreateFileW(rel, 0,
+ FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
+ OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
+ if (hnd == INVALID_HANDLE_VALUE) {
+ errno = err_win_to_posix(GetLastError());
+ return PHANTOM_SYMLINK_RETRY;
+ }
+
+ if (!GetFileInformationByHandle(hnd, &fdata)) {
+ errno = err_win_to_posix(GetLastError());
+ CloseHandle(hnd);
+ return PHANTOM_SYMLINK_RETRY;
+ }
+ CloseHandle(hnd);
+
+ /* if target exists and is a file, we're done */
+ if (!(fdata.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY))
+ return PHANTOM_SYMLINK_DONE;
+
+ /* otherwise recreate the symlink with directory flag */
+ if (DeleteFileW(wlink) && CreateSymbolicLinkW(wlink, wtarget, 1))
+ return PHANTOM_SYMLINK_DIRECTORY;
+
+ errno = err_win_to_posix(GetLastError());
+ return PHANTOM_SYMLINK_RETRY;
+}
+
+/* keep track of newly created symlinks to non-existing targets */
+struct phantom_symlink_info {
+ struct phantom_symlink_info *next;
+ wchar_t *wlink;
+ wchar_t *wtarget;
+};
+
+static struct phantom_symlink_info *phantom_symlinks = NULL;
+static CRITICAL_SECTION phantom_symlinks_cs;
+
+static void process_phantom_symlinks(void)
+{
+ struct phantom_symlink_info *current, **psi;
+ EnterCriticalSection(&phantom_symlinks_cs);
+ /* process phantom symlinks list */
+ psi = &phantom_symlinks;
+ while ((current = *psi)) {
+ enum phantom_symlink_result result = process_phantom_symlink(
+ current->wtarget, current->wlink);
+ if (result == PHANTOM_SYMLINK_RETRY) {
+ psi = ¤t->next;
+ } else {
+ /* symlink was processed, remove from list */
+ *psi = current->next;
+ free(current);
+ /* if symlink was a directory, start over */
+ if (result == PHANTOM_SYMLINK_DIRECTORY)
+ psi = &phantom_symlinks;
+ }
+ }
+ LeaveCriticalSection(&phantom_symlinks_cs);
+}
+
/* Normalizes NT paths as returned by some low-level APIs. */
static wchar_t *normalize_ntpath(wchar_t *wbuf)
{
@@ -479,6 +604,8 @@ int mingw_mkdir(const char *path, int mode UNUSED)
if (xutftowcs_path(wpath, path) < 0)
return -1;
ret = _wmkdir(wpath);
+ if (!ret)
+ process_phantom_symlinks();
if (!ret && needs_hiding(path))
return set_hidden_flag(wpath, 1);
return ret;
@@ -2723,6 +2850,42 @@ int symlink(const char *target, const char *link)
errno = err_win_to_posix(GetLastError());
return -1;
}
+
+ /* convert to directory symlink if target exists */
+ switch (process_phantom_symlink(wtarget, wlink)) {
+ case PHANTOM_SYMLINK_RETRY: {
+ /* if target doesn't exist, add to phantom symlinks list */
+ wchar_t wfullpath[MAX_PATH];
+ struct phantom_symlink_info *psi;
+
+ /* convert to absolute path to be independent of cwd */
+ len = GetFullPathNameW(wlink, MAX_PATH, wfullpath, NULL);
+ if (!len || len >= MAX_PATH) {
+ errno = err_win_to_posix(GetLastError());
+ return -1;
+ }
+
+ /* over-allocate and fill phantom_symlink_info structure */
+ psi = xmalloc(sizeof(struct phantom_symlink_info)
+ + sizeof(wchar_t) * (len + wcslen(wtarget) + 2));
+ psi->wlink = (wchar_t *)(psi + 1);
+ wcscpy(psi->wlink, wfullpath);
+ psi->wtarget = psi->wlink + len + 1;
+ wcscpy(psi->wtarget, wtarget);
+
+ EnterCriticalSection(&phantom_symlinks_cs);
+ psi->next = phantom_symlinks;
+ phantom_symlinks = psi;
+ LeaveCriticalSection(&phantom_symlinks_cs);
+ break;
+ }
+ case PHANTOM_SYMLINK_DIRECTORY:
+ /* if we created a dir symlink, process other phantom symlinks */
+ process_phantom_symlinks();
+ break;
+ default:
+ break;
+ }
return 0;
}
@@ -3424,6 +3587,7 @@ int wmain(int argc, const wchar_t **wargv)
/* initialize critical section for waitpid pinfo_t list */
InitializeCriticalSection(&pinfo_cs);
+ InitializeCriticalSection(&phantom_symlinks_cs);
/* set up default file mode and file modes for stdin/out/err */
_fmode = _O_BINARY;
--
gitgitgadget
next prev parent reply other threads:[~2026-01-09 20:05 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-17 14:08 [PATCH 00/18] Support symbolic links on Windows Johannes Schindelin via GitGitGadget
2025-12-17 14:08 ` [PATCH 01/18] mingw: don't call `GetFileAttributes()` twice in `mingw_lstat()` Karsten Blees via GitGitGadget
2025-12-18 10:34 ` Johannes Sixt
2025-12-17 14:08 ` [PATCH 02/18] mingw: implement `stat()` with symlink support Karsten Blees via GitGitGadget
2025-12-18 10:44 ` Johannes Sixt
2026-01-09 20:04 ` Johannes Schindelin
2025-12-17 14:08 ` [PATCH 03/18] mingw: drop the separate `do_lstat()` function Karsten Blees via GitGitGadget
2025-12-18 10:48 ` Johannes Sixt
2025-12-17 14:08 ` [PATCH 04/18] mingw: let `mingw_lstat()` error early upon problems with reparse points Karsten Blees via GitGitGadget
2025-12-17 14:08 ` [PATCH 05/18] mingw: teach dirent about symlinks Karsten Blees via GitGitGadget
2025-12-17 14:08 ` [PATCH 06/18] mingw: compute the correct size for symlinks in `mingw_lstat()` Bill Zissimopoulos via GitGitGadget
2025-12-17 14:08 ` [PATCH 07/18] mingw: factor out the retry logic Karsten Blees via GitGitGadget
2025-12-17 14:08 ` [PATCH 08/18] mingw: change default of `core.symlinks` to false Karsten Blees via GitGitGadget
2025-12-17 14:08 ` [PATCH 09/18] mingw: add symlink-specific error codes Karsten Blees via GitGitGadget
2025-12-17 14:08 ` [PATCH 10/18] mingw: handle symlinks to directories in `mingw_unlink()` Karsten Blees via GitGitGadget
2025-12-18 2:49 ` Ben Knoble
2026-01-09 20:04 ` Johannes Schindelin
2025-12-17 14:08 ` [PATCH 11/18] mingw: support renaming symlinks Karsten Blees via GitGitGadget
2025-12-18 17:44 ` Johannes Sixt
2026-01-09 20:04 ` Johannes Schindelin
2025-12-17 14:08 ` [PATCH 12/18] mingw: allow `mingw_chdir()` to change to symlink-resolved directories Karsten Blees via GitGitGadget
2025-12-17 14:08 ` [PATCH 13/18] mingw: implement `readlink()` Karsten Blees via GitGitGadget
2025-12-18 18:13 ` Johannes Sixt
2026-01-09 20:04 ` Johannes Schindelin
2025-12-17 14:08 ` [PATCH 14/18] mingw: implement basic `symlink()` functionality (file symlinks only) Karsten Blees via GitGitGadget
2025-12-17 14:08 ` [PATCH 15/18] mingw: add support for symlinks to directories Karsten Blees via GitGitGadget
2025-12-17 14:08 ` [PATCH 16/18] mingw: try to create symlinks without elevated permissions Johannes Schindelin via GitGitGadget
2025-12-17 14:08 ` [PATCH 17/18] mingw: emulate `stat()` a little more faithfully Johannes Schindelin via GitGitGadget
2025-12-17 14:08 ` [PATCH 18/18] mingw: special-case index entries for symlinks with buggy size Johannes Schindelin via GitGitGadget
2025-12-18 0:00 ` [PATCH 00/18] Support symbolic links on Windows Junio C Hamano
2025-12-18 18:51 ` Johannes Sixt
2025-12-18 19:33 ` Karsten Blees
2026-01-09 20:04 ` [PATCH v2 " Johannes Schindelin via GitGitGadget
2026-01-09 20:04 ` [PATCH v2 01/18] mingw: don't call `GetFileAttributes()` twice in `mingw_lstat()` Karsten Blees via GitGitGadget
2026-01-09 20:04 ` [PATCH v2 02/18] mingw: implement `stat()` with symlink support Karsten Blees via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 03/18] mingw: drop the separate `do_lstat()` function Karsten Blees via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 04/18] mingw: let `mingw_lstat()` error early upon problems with reparse points Karsten Blees via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 05/18] mingw: teach dirent about symlinks Karsten Blees via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 06/18] mingw: compute the correct size for symlinks in `mingw_lstat()` Bill Zissimopoulos via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 07/18] mingw: factor out the retry logic Karsten Blees via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 08/18] mingw: change default of `core.symlinks` to false Karsten Blees via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 09/18] mingw: add symlink-specific error codes Karsten Blees via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 10/18] mingw: handle symlinks to directories in `mingw_unlink()` Karsten Blees via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 11/18] mingw: support renaming symlinks Karsten Blees via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 12/18] mingw: allow `mingw_chdir()` to change to symlink-resolved directories Karsten Blees via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 13/18] mingw: implement `readlink()` Karsten Blees via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 14/18] mingw: implement basic `symlink()` functionality (file symlinks only) Karsten Blees via GitGitGadget
2026-01-09 20:05 ` Karsten Blees via GitGitGadget [this message]
2026-01-09 20:05 ` [PATCH v2 16/18] mingw: try to create symlinks without elevated permissions Johannes Schindelin via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 17/18] mingw: emulate `stat()` a little more faithfully Johannes Schindelin via GitGitGadget
2026-01-09 20:05 ` [PATCH v2 18/18] mingw: special-case index entries for symlinks with buggy size Johannes Schindelin via GitGitGadget
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