fsmonitor-settings: remote repos on Windows are incompatible

Teach Git to detect remote working directories on Windows and mark them as
incompatible with FSMonitor.

With this `git fsmonitor--daemon run` will error out with a message like it
does for bare repos.

Client commands, such as `git status`, will not attempt to start the daemon.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/compat/fsmonitor/fsm-settings-win32.c b/compat/fsmonitor/fsm-settings-win32.c
index ee78bba38e322d6c57ebf3df3396f11b77e59680..907655720bb41e303e5ce86ae367778608b08548 100644 (file)
--- a/compat/fsmonitor/fsm-settings-win32.c
+++ b/compat/fsmonitor/fsm-settings-win32.c
@@ -2,6 +2,7 @@
 #include "config.h"
 #include "repository.h"
 #include "fsmonitor-settings.h"
+#include "fsmonitor.h"
 
 /*
  * VFS for Git is incompatible with FSMonitor.
@@ -23,6 +24,103 @@ static enum fsmonitor_reason check_vfs4git(struct repository *r)
        return FSMONITOR_REASON_OK;
 }
 
+/*
+ * Remote working directories are problematic for FSMonitor.
+ *
+ * The underlying file system on the server machine and/or the remote
+ * mount type dictates whether notification events are available at
+ * all to remote client machines.
+ *
+ * Kernel differences between the server and client machines also
+ * dictate the how (buffering, frequency, de-dup) the events are
+ * delivered to client machine processes.
+ *
+ * A client machine (such as a laptop) may choose to suspend/resume
+ * and it is unclear (without lots of testing) whether the watcher can
+ * resync after a resume.  We might be able to treat this as a normal
+ * "events were dropped by the kernel" event and do our normal "flush
+ * and resync" --or-- we might need to close the existing (zombie?)
+ * notification fd and create a new one.
+ *
+ * In theory, the above issues need to be addressed whether we are
+ * using the Hook or IPC API.
+ *
+ * So (for now at least), mark remote working directories as
+ * incompatible.
+ *
+ * Notes for testing:
+ *
+ * (a) Windows allows a network share to be mapped to a drive letter.
+ *     (This is the normal method to access it.)
+ *
+ *     $ NET USE Z: \\server\share
+ *     $ git -C Z:/repo status
+ *
+ * (b) Windows allows a network share to be referenced WITHOUT mapping
+ *     it to drive letter.
+ *
+ *     $ NET USE \\server\share\dir
+ *     $ git -C //server/share/repo status
+ *
+ * (c) Windows allows "SUBST" to create a fake drive mapping to an
+ *     arbitrary path (which may be remote)
+ *
+ *     $ SUBST Q: Z:\repo
+ *     $ git -C Q:/ status
+ *
+ * (d) Windows allows a directory symlink to be created on a local
+ *     file system that points to a remote repo.
+ *
+ *     $ mklink /d ./link //server/share/repo
+ *     $ git -C ./link status
+ */
+static enum fsmonitor_reason check_remote(struct repository *r)
+{
+       wchar_t wpath[MAX_PATH];
+       wchar_t wfullpath[MAX_PATH];
+       size_t wlen;
+       UINT driveType;
+
+       /*
+        * Do everything in wide chars because the drive letter might be
+        * a multi-byte sequence.  See win32_has_dos_drive_prefix().
+        */
+       if (xutftowcs_path(wpath, r->worktree) < 0)
+               return FSMONITOR_REASON_ERROR;
+
+       /*
+        * GetDriveTypeW() requires a final slash.  We assume that the
+        * worktree pathname points to an actual directory.
+        */
+       wlen = wcslen(wpath);
+       if (wpath[wlen - 1] != L'\\' && wpath[wlen - 1] != L'/') {
+               wpath[wlen++] = L'\\';
+               wpath[wlen] = 0;
+       }
+
+       /*
+        * Normalize the path.  If nothing else, this converts forward
+        * slashes to backslashes.  This is essential to get GetDriveTypeW()
+        * correctly handle some UNC "\\server\share\..." paths.
+        */
+       if (!GetFullPathNameW(wpath, MAX_PATH, wfullpath, NULL))
+               return FSMONITOR_REASON_ERROR;
+
+       driveType = GetDriveTypeW(wfullpath);
+       trace_printf_key(&trace_fsmonitor,
+                        "DriveType '%s' L'%ls' (%u)",
+                        r->worktree, wfullpath, driveType);
+
+       if (driveType == DRIVE_REMOTE) {
+               trace_printf_key(&trace_fsmonitor,
+                                "check_remote('%s') true",
+                                r->worktree);
+               return FSMONITOR_REASON_REMOTE;
+       }
+
+       return FSMONITOR_REASON_OK;
+}
+
 enum fsmonitor_reason fsm_os__incompatible(struct repository *r)
 {
        enum fsmonitor_reason reason;
@@ -31,5 +129,9 @@ enum fsmonitor_reason fsm_os__incompatible(struct repository *r)
        if (reason != FSMONITOR_REASON_OK)
                return reason;
 
+       reason = check_remote(r);
+       if (reason != FSMONITOR_REASON_OK)
+               return reason;
+
        return FSMONITOR_REASON_OK;
 }