linkup

commit a286b18428747eafbb6923b86fe5f25c3f70f7bf
Author: Louis Burda <quent.burda@gmail.com>
Date:   Thu, 20 Oct 2022 01:16:22 +0200

Initial prototype

Diffstat:
A
.gitignore
 | 
1
+
A
Makefile
 | 
14
++++++++++++++
A
linkup.c
 | 
153
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

3 files changed, 168 insertions(+), 0 deletions(-)
diff --git a/.gitignore b/.gitignore
@@ -0,0 +1 @@
+linkup
diff --git a/Makefile b/Makefile
@@ -0,0 +1,14 @@
+all: linkup
+
+clean:
+	rm -f linkup
+
+linkup: linkup.c
+
+install: linkup
+	install -m755 linkup -T "$(DESTDIR)$(PREFIX)$(BINDIR)/linkup"
+
+uninstall:
+	rm -f "$(DESTDIR)$(PREFIX)$(BINDIR)/linkup"
+
+.PHONY: all clean install uninstall
diff --git a/linkup.c b/linkup.c
@@ -0,0 +1,153 @@
+#include <linux/limits.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <dirent.h>
+#include <unistd.h>
+#include <err.h>
+#include <errno.h>
+#include <string.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+static const char usage[] = "linkup [-h] [-x FILE..] SOURCE DEST";
+
+static bool force;
+
+bool
+exists(int dirfd, const char *path)
+{
+	struct stat attr;
+
+	return !fstatat(dirfd, path, &attr, AT_SYMLINK_NOFOLLOW);
+}
+
+void
+removeall(int pfd, const char *path)
+{
+	struct dirent *ent;
+	struct stat attr;
+	DIR *dir;
+	int fd;
+
+	if (fstatat(pfd, path, &attr, AT_SYMLINK_NOFOLLOW) < 0) {
+		if (errno == ENOENT) return;
+		err(1, "fstatat");
+	}
+
+	if ((attr.st_mode & S_IFMT) == S_IFDIR) {
+		fd = openat(pfd, path, 0);
+		dir = fdopendir(fd);
+		if (!dir) err(1, "opendir");
+		while ((ent = readdir(dir)))
+			removeall(fd, ent->d_name);
+		closedir(dir);
+	}
+
+	unlinkat(pfd, path, AT_REMOVEDIR);
+}
+
+int
+main(int argc, const char **argv)
+{
+	char spbuf[PATH_MAX], dpbuf[PATH_MAX];
+	char spath[PATH_MAX], dpath[PATH_MAX];
+	struct dirent *ent;
+	struct stat attr;
+	const char *sarg, *darg;
+	const char **arg;
+	DIR *sdir, *ddir;
+	const char **ignored;
+	int ignorecnt;
+	int ignorecap;
+	int i;
+
+	ignored = NULL;
+	ignorecap = 0;
+	ignorecnt = 0;
+
+	force = false;
+	sarg = darg = NULL;
+	for (arg = &argv[1]; *arg; arg++) {
+		if (!strcmp(*arg, "-x")) {
+			if (ignorecnt == ignorecap) {
+				ignorecap = (ignorecap + 1) * 2;
+				ignored = realloc(ignored,
+					ignorecap * sizeof(const char *));
+			}
+			ignored[ignorecnt] = *arg;
+			ignorecnt++;
+		} else if (!strcmp(*arg, "-f")) {
+			force = true;
+		} else if (!sarg) {
+			sarg = *arg;
+		} else if (!darg) {
+			darg = *arg;
+		} else {
+			printf("Usage: %s\n", usage);
+			return 0;
+		}
+	}
+
+	if (!sarg || !darg) {
+		fprintf(stderr, "Usage: %s\n", usage);
+		return 1;
+	}
+
+	if (!realpath(sarg, spath))
+		err(1, "realpath src");
+
+	if (!realpath(darg, dpath))
+		err(1, "realpath dst");
+
+	sdir = opendir(spath);
+	if (!sdir) err(1, "opendir src");
+
+	ddir = opendir(dpath);
+	if (!ddir) err(1, "opendir dst");
+
+	while ((ent = readdir(sdir))) {
+		/* skip ignored files */
+		for (i = 0; i < ignorecnt; i++) {
+			if (!strcmp(ignored[i], ent->d_name))
+				break;
+		}
+		if (i != ignorecnt) continue;
+
+		/* skip default directories */
+		if (!strcmp(ent->d_name, "."))
+			continue;
+		if (!strcmp(ent->d_name, ".."))
+			continue;
+
+		/* ensure link destination does not exist */
+		if (!fstatat(dirfd(ddir), ent->d_name,
+				&attr, AT_SYMLINK_NOFOLLOW)) {
+			if ((attr.st_mode & S_IFMT) != S_IFLNK && !force)
+				errx(1, "dst %s already exists\n", ent->d_name);
+		}
+		removeall(dirfd(ddir), ent->d_name);
+
+		/* create link */
+		snprintf(spbuf, PATH_MAX, "%s/%s", spath, ent->d_name);
+		snprintf(dpbuf, PATH_MAX, "%s/%s", dpath, ent->d_name);
+		if (symlink(spbuf, dpbuf) < 0)
+			err(1, "link");
+	}
+
+	/* clean dangling symlinks */
+	while ((ent = readdir(ddir))) {
+		if (ent->d_type != DT_LNK)
+			continue;
+		snprintf(dpbuf, PATH_MAX, "%s/%s", dpath, ent->d_name);
+		if (readlink(dpbuf, dpbuf, PATH_MAX) < 0)
+			err(1, "readlink");
+		realpath(dpbuf, dpbuf);
+		if (strncmp(dpbuf, spath, strlen(spath)))
+			break;
+		if (fstatat(dirfd(ddir), ent->d_name, &attr, 0) < 0)
+			unlinkat(dirfd(ddir), ent->d_name, 0);
+	}
+
+	free(ignored);
+}