Support symbolic links on Windows #2018
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The 'symref transaction supports symlinks' test case is guarded by the `SYMLINK` prerequisite because `core.prefersymlinkrefs = true` requires symbolic links to be supported. However, the `preferSymlinkRefs` feature is not supported on Windows, therefore this test case needs the `MINGW` prerequisite, too. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
The MSYS2 runtime (which inherits this trait from the Cygwin runtime, and which is used by Git for Windows' Bash to emulate POSIX functionality on Windows, the same Bash that is also used to run Git's test suite on Windows) has a mode where it can create native symbolic links on Windows. Naturally, this is a bit of a strange feature, given that Cygwin goes out of its way to support Unix-like paths even if no Win32 program understands those, and the symbolic links have to use Win32 paths instead (which Win32 programs understand very well). As a consequence, the symbolic link targets get normalized before the links are created. This results in certain quirks that Git's test suite is ill equipped to accommodate (because Git's test suite expects to be able to use Unix-like paths even on Windows). The test script t1006-cat-file.sh contains two prime examples, two test cases that need to skip a couple assertions because they are simply wrong in the context of Git for Windows. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
In Git for Windows, the gitdir is canonicalized so that even when the gitdir is specified via a symbolic link, the `gitdir:` conditional include will only match the real directory path. Unfortunately, t1305 codifies a different behavior in two test cases, which are hereby skipped on Windows. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
The device `/dev/null` does not exist on Windows, it's called `NUL` there. Calling `ln -s /dev/null my-symlink` in a symlink-enabled MSYS2 Bash will therefore literally link to a file or directory called `null` that is supposed to be in the current drive's top-level `dev` directory. Which typically does not exist. The test, however, really wants the created symbolic link to point to the NUL device. Let's instead use the `mklink` utility on Windows to perform that job, and keep using `ln -s /dev/null <target>` on non-Windows platforms. While at it, add the missing `SYMLINKS` prereq because this test _still_ would not pass on Windows before support for symbolic links is upstreamed from Git for Windows. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git's test suite's relies on Unix shell scripting, which is understandable, of course, given Git's firm roots (and indeed, ongoing focus) on Linux. This fact, combined with Unix shell scripting's natural habitat -- which is, naturally... *drumroll*... Unix -- often has unintended side effects, where developers expect the test suite to run in a Unix environment, which is an incorrect assumption. One instance of this problem can be observed in the 'difftool --dir-diff handles modified symlinks' test case in `t7800-difftool.sh`, which assumes that all absolute paths start with a forward slash. That assumption is incorrect in general, e.g. on Windows, where absolute paths have many shapes and forms, none of which starts with a forward slash. The only saving grace is that this test case is currently not run on Windows because of the `SYMLINK` prerequisite. However, I am currently working towards upstreaming symbolic link support from Git for Windows to upstream Git, which will put a crack into that saving grace. Let's change that test case so that it does not rely on absolute paths (which are passed to the "external command" `ls` as parameters and are therefore part of its output, and which the test case wants to filter out before verifying that the output is as expected) starting with a forward slash. Let's instead rely on the much more reliable fact that `ls` will output the path in a line that ends in a colon, and simply filter out those lines by matching said colon instead. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
* js/test-symlink-windows: t7800: work around the MSYS path conversion on Windows t6423: introduce Windows-specific handling for symlinking to /dev/null t1305: skip symlink tests that do not apply to Windows t1006: accommodate for symlink support in MSYS2 t0600: fix incomplete prerequisite for a test case t0301: another fix for Windows compatibility t0001: handle `diff --no-index` gracefully mingw: special-case `open(symlink, O_CREAT | O_EXCL)` apply: symbolic links lack a "trustable executable bit" t9700: accommodate for Windows paths
As pointed out in git-for-windows#1676, the `git rev-parse --is-inside-work-tree` command currently fails when the current directory's path contains symbolic links. The underlying reason for this bug is that `getcwd()` is supposed to resolve symbolic links, but our `mingw_getcwd()` implementation did not. We do have all the building blocks for that, though: the `GetFinalPathByHandleW()` function will resolve symbolic links. However, we only called that function if `GetLongPathNameW()` failed, for historical reasons: the latter function was supported for a long time, but the former API function was introduced only with Windows Vista, and we used to support also Windows XP. With that support having been dropped, we are free to call the symbolic link-resolving function right away. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
In Git for Windows, `has_symlinks` is set to 0 by default. Therefore, we need to parse the config setting `core.symlinks` to know if it has been set to `true`. In `git init`, we must do that before copying the templates because they might contain symbolic links. Even if the support for symbolic links on Windows has not made it to upstream Git yet, we really should make sure that all the `core.*` settings are parsed before proceeding, as they might very well change the behavior of `git init` in a way the user intended. This fixes git-for-windows#3414 Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `strbuf_readlink()` function calls `readlink()`` twice if the hint argument specifies the exact size of the link target (e.g. by passing stat.st_size as returned by `lstat()`). This is necessary because `readlink(..., hint) == hint` could mean that the buffer was too small. Use `hint + 1` as buffer size to prevent this. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `strbuf_readlink()` function refuses to read link targets that exceed PATH_MAX (even if a sufficient size was specified by the caller). As some platforms (*cough* Windows *cough*) support longer paths, remove this restriction (similar to `strbuf_getcwd()`). Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Currently, this function hard-codes the directory separator as the forward slash. However, on Windows the backslash character is valid, too. And we want to call this function in the upcoming support for symlinks on Windows with the symlink targets (which naturally use the canonical directory separator on Windows, which is _not_ the forward slash). Prepare that function to be useful also in that context. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
The Win32 API function `GetFileAttributes()` cannot handle paths with trailing dir separators. The current `mingw_stat()`/`mingw_lstat()` implementation calls `GetFileAttributes()` twice if the path has trailing slashes (first with the original path that was passed as function parameter, and and a second time with a path copy with trailing '/' removed). With the conversion to wide Unicode, we get the length of the path for free, and also have a (wide char) buffer that can be modified. This makes it easy to avoid that extraneous Win32 API call. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
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There are issues in commit ca10b27: |
With respect to symlinks, the current `mingw_stat()` implementation is almost identical to `mingw_lstat()`: except for the file type (`st_mode & S_IFMT`), it returns information about the link rather than the target. Implement `mingw_stat()` by opening the file handle requesting minimal permissions, and then calling `GetFileInformationByHandle()` on it. This way, all links are resolved by the Windows file system layer. If symlinks are disabled, use `mingw_lstat()` as before, but fail with `ELOOP` if a symlink would have to be resolved. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
With the new `mingw_stat()` implementation, `do_lstat()` is only called from `mingw_lstat()` (with the function parameter `follow == 0`). Remove the extra function and the old `mingw_stat()`-specific (`follow == 1`) logic. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
When obtaining lstat information for reparse points, we need to call `FindFirstFile()` in addition to `GetFileInformationEx()` to obtain the type of the reparse point (symlink, mount point etc.). However, currently there is no error handling whatsoever if `FindFirstFile()` fails. Call `FindFirstFile()` before modifying the `stat *buf` output parameter and error out if the call fails. Note: The `FindFirstFile()` return value includes all the data that we get from `GetFileAttributesEx()`, so we could replace `GetFileAttributesEx()` with `FindFirstFile()`. We don't do that because `GetFileAttributesEx()` is about twice as fast for single files. I.e. we only pay the extra cost of calling `FindFirstFile()` in the rare case that we encounter a reparse point. Please also note that the indentation the remaining reparse point code changed, and hence the best way to look at this diff is with `--color-moved -w`. That code was _not_ moved because a subsequent commit will move it to an altogether different function, anyway. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Move the `S_IFLNK` detection to `file_attr_to_st_mode()`. Implement `DT_LNK` detection in dirent.c's `readdir()` function. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
POSIX specifies that upon successful return from `lstat()`: "the value of the st_size member shall be set to the length of the pathname contained in the symbolic link not including any terminating null byte". Git typically doesn't trust the `stat.st_size` member of symlinks (e.g. see `strbuf_readlink()`). Therefore, it is tempting to save on the extra overhead of opening and reading the reparse point merely to calculate the exact size of the link target. This is, in fact, what Git for Windows did, from May 2015 to May 2020. At least almost: some functions take shortcuts if `st_size` is 0 (e.g. `diff_populate_filespec()`), hence Git for Windows hard-coded the length of all symlinks to MAX_PATH. This did cause problems, though, specifically in Git repositories that were also accessed by Git for Cygwin or Git for WSL. For example, doing `git reset --hard` using Git for Windows would update the size of symlinks in the index to be MAX_PATH; at a later time Git for Cygwin or Git for WSL would find that symlinks have changed size during `git status` and update the index. And then Git for Windows would think that the index needs to be updated. Even if the symlinks did not, in fact, change. To avoid that, the correct size must be determined. Signed-off-by: Bill Zissimopoulos <billziss@navimatics.com> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
In several places, Git's Windows-specific code follows the pattern where it tries to perform an operation, and retries several times when that operation fails, sleeping an increasing amount of time, before finally giving up and asking the user whether to rety (after, say, closing an editor that held a handle to a file, preventing the operation from succeeding). This logic is a bit hard to use, and inconsistent: `mingw_unlink()` and `mingw_rmdir()` duplicate the code to retry, and both of them do so incompletely. They also do not restore `errno` if the user answers 'no'. Introduce a `retry_ask_yes_no()` helper function that handles retry with small delay, asking the user, and restoring `errno`. Note that in `mingw_unlink()`, we include the `_wchmod()` call in the retry loop (which may fail if the file is locked exclusively). In `mingw_rmdir()`, we include special error handling in the retry loop. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Symlinks on Windows don't work the same way as on Unix systems. For example, there are different types of symlinks for directories and files, and unless using a recent-ish Windows version in Developer Mode, creating symlinks requires administrative privileges. By default, disable symlink support on Windows. That is, users explicitly have to enable it with `git config [--system|--global] core.symlinks true`; For convenience, `git init` (and `git clone`) will perform a test whether the current setup allows creating symlinks and will configure that setting in the repository config. The test suite ignores system / global config files. Allow testing *with* symlink support by checking if native symlinks are enabled in MSYS2 (via setting the special environment variable `MSYS=winsymlinks:nativestrict` to ask the MSYS2 runtime to enable creating symlinks). Note: This assumes that Git's test suite is run in MSYS2's Bash, which is true for the time being (an experiment to switch to BusyBox-w32 failed due to the experimental nature of BusyBox-w32). Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
The Win32 API calls do not set `errno`; Instead, error codes for failed operations must be obtained via the `GetLastError()` function. Git would not know what to do with those error values, though, which is why Git's Windows compatibility layer translates them to `errno` values. Let's handle a couple of symlink-related error codes that will become relevant with the upcoming support for symlinks on Windows. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
The `_wunlink()` and `DeleteFileW()` functions refuse to delete symlinks to directories on Windows; The error code woutl be `ERROR_ACCESS_DENIED` in that case. Take that error code as an indicator that we need to try `_wrmdir()` as well. In the best case, it will remove a symlink. In the worst case, it will fail with the same error code again. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Older MSVCRT's `_wrename()` function cannot rename symlinks over existing files: it returns success without doing anything. Newer MSVCR*.dll versions probably do not share this problem: according to CRT sources, they just call `MoveFileEx()` with the `MOVEFILE_COPY_ALLOWED` flag. Avoid the `_wrename()` call, and go with directly calling `MoveFileEx()`, with proper error handling of course. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
If symlinks are enabled, resolve all symlinks when changing directories, as required by POSIX. Note: Git's `real_path()` function bases its link resolution algorithm on this property of `chdir()`. Unfortunately, the current directory on Windows is limited to only MAX_PATH (260) characters. Therefore using symlinks and long paths in combination may be problematic. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.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`. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Implement `symlink()`. This implementation always creates _file_ symlinks (remember: Windows discerns between symlinks pointing to directories and those pointing to files). Support for directory symlinks will be added in a subseqeuent commit. This implementation fails with `ENOSYS` if symlinks are disabled or unsupported. Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
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 <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
As of Windows 10 Build 14972 in Developer Mode, a new flag is supported by `CreateSymbolicLink()` to create symbolic links even when running outside of an elevated session (which was previously required). This new flag is called `SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE` and has the numeric value 0x02. Previous Windows 10 versions will not understand that flag and return an `ERROR_INVALID_PARAMETER`, therefore we have to be careful to try passing that flag only when the build number indicates that it is supported. For more information about the new flag, see this blog post: https://blogs.windows.com/buildingapps/2016/12/02/symlinks-windows-10/ Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
When creating directories via `safe_create_leading_directories()`, we might encounter an already-existing directory which is not readable by the current user. To handle that situation, Git's code calls `stat()` to determine whether we're looking at a directory. In such a case, `CreateFile()` will fail, though, no matter what, and consequently `mingw_stat()` will fail, too. But POSIX semantics seem to still allow `stat()` to go forward. So let's call `mingw_lstat()` to the rescue if we fail to get a file handle due to denied permission in `mingw_stat()`, and fill the stat info that way. We need to be careful to not allow this to go forward in case that we're looking at a symbolic link: to resolve the link, we would still have to create a file handle, and we just found out that we cannot. Therefore, `stat()` still needs to fail with `EACCES` in that case. This fixes git-for-windows#2531. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
In git-for-windows#2637, we fixed a bug where symbolic links' target path sizes were recorded incorrectly in the index. The downside of this fix was that every user with tracked symbolic links in their checkouts would see them as modified in `git status`, but not in `git diff`, and only a `git add <path>` (or `git add -u`) would "fix" this. Let's do better than that: we can detect that situation and simply pretend that a symbolic link with a known bad size (or a size that just happens to be that bad size, a _very_ unlikely scenario because it would overflow our buffers due to the trailing NUL byte) means that it needs to be re-checked as if we had just checked it out. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
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This finally upstreams Git for Windows' support for Windows' branch of symbolic links, which has been maturing since 2015. It is based off of
js/prep-symlink-windows.