fsmonitor: refactor filesystem checks to common interface

Provide a common interface for getting basic filesystem information
including filesystem type and whether the filesystem is remote.

Refactor existing code for getting basic filesystem info and detecting
remote file systems to the new interface.

Refactor filesystem checks to leverage new interface. For macOS,
error-out if the Unix Domain socket (UDS) file is on a remote
filesystem.

Signed-off-by: Eric DeCosta <edecosta@mathworks.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/fsmonitor-settings.c b/fsmonitor-settings.c
index 464424a1e9..d288cbad47 100644
--- a/fsmonitor-settings.c
+++ b/fsmonitor-settings.c
@@ -2,6 +2,7 @@
 #include "config.h"
 #include "repository.h"
 #include "fsmonitor-settings.h"
+#include "fsmonitor-path-utils.h"
 
 /*
  * We keep this structure defintion private and have getters
@@ -13,6 +14,52 @@ struct fsmonitor_settings {
 	char *hook_path;
 };
 
+/*
+ * 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 unless 'fsmonitor.allowRemote' is true.
+ *
+ */
+#ifdef HAVE_FSMONITOR_OS_SETTINGS
+static enum fsmonitor_reason check_remote(struct repository *r)
+{
+	int allow_remote = -1; /* -1 unset, 0 not allowed, 1 allowed */
+	int is_remote = fsmonitor__is_fs_remote(r->worktree);
+
+	switch (is_remote) {
+		case 0:
+			return FSMONITOR_REASON_OK;
+		case 1:
+			repo_config_get_bool(r, "fsmonitor.allowremote", &allow_remote);
+			if (allow_remote < 1)
+				return FSMONITOR_REASON_REMOTE;
+			else
+				return FSMONITOR_REASON_OK;
+		default:
+			return FSMONITOR_REASON_ERROR;
+	}
+}
+#endif
+
 static enum fsmonitor_reason check_for_incompatible(struct repository *r)
 {
 	if (!r->worktree) {
@@ -27,6 +74,9 @@ static enum fsmonitor_reason check_for_incompatible(struct repository *r)
 	{
 		enum fsmonitor_reason reason;
 
+		reason = check_remote(r);
+		if (reason != FSMONITOR_REASON_OK)
+			return reason;
 		reason = fsm_os__incompatible(r);
 		if (reason != FSMONITOR_REASON_OK)
 			return reason;