fd: Factor out inheriting FDs code

We have two places where we lookup the inherited-fd list
by name and dup() the descriptor found. I propose to factor
out this piece in a single inherited_fd() call. When
we will want to support inheritance for sockets or any
other files we'll simply add the inherited_fd() call
there.

I'm also thinking about moving the call to inherited_fd
into generic level, but the open_path() routine doesn't
allow to do it in a simple manner.

Also we have not yet finished issue with files-vs-inodes
mapping. Keeping all the logic in one function should
make the solution simpler.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

files-reg.c

@@ -919,22 +919,10 @@ int open_path(struct file_desc *d,
 	int tmp, mntns_root;
 	char *orig_path = NULL;
 
-	rfi = container_of(d, struct reg_file_info, d);
-
-	tmp = inherit_fd_lookup_id(rfi->path);
-	if (tmp >= 0) {
-		int fd;
-
-		fd = dup(tmp);
-		if (fd == -1) {
-			pr_perror("Can't dup inherit fd %d\n", fd);
-			return -1;
-		}
-		pr_info("File %s will be restored from fd %d duped from inherit fd %d\n",
-			rfi->path, fd, tmp);
-		return fd;
-	}
+	if (inherited_fd(d, &tmp))
+		return tmp;
 
+	rfi = container_of(d, struct reg_file_info, d);
 	if (rfi->remap) {
 		mutex_lock(ghost_file_mutex);
 		if (rfi->remap->is_dir) {
@@ -1138,10 +1126,19 @@ static int open_fe_fd(struct file_desc *fd)
 	return open_path(fd, do_open_reg, NULL);
 }
 
+static char *reg_file_path(struct file_desc *d, char *buf, size_t s)
+{
+	struct reg_file_info *rfi;
+
+	rfi = container_of(d, struct reg_file_info, d);
+	return rfi->path;
+}
+
 static struct file_desc_ops reg_desc_ops = {
 	.type = FD_TYPES__REG,
 	.open = open_fe_fd,
 	.collect_fd = collect_reg_fd,
+	.name = reg_file_path,
 };
 
 struct file_desc *try_collect_special_file(u32 id, int optional)

files.c

@@ -1344,7 +1344,7 @@ void inherit_fd_log(void)
 /*
  * Look up the inherit fd list by a file identifier.
  */
-int inherit_fd_lookup_id(char *id)
+static int inherit_fd_lookup_id(char *id)
 {
 	int ret;
 	struct inherit_fd *inh;
@@ -1363,6 +1363,28 @@ int inherit_fd_lookup_id(char *id)
 	return ret;
 }
 
+bool inherited_fd(struct file_desc *d, int *fd_p)
+{
+	char buf[32], *id_str;
+	int i_fd;
+
+	if (!d->ops->name)
+		return false;
+
+	id_str = d->ops->name(d, buf, sizeof(buf));
+	i_fd = inherit_fd_lookup_id(id_str);
+	if (i_fd < 0)
+		return false;
+
+	*fd_p = dup(i_fd);
+	if (*fd_p < 0)
+		pr_perror("Inherit fd DUP failed");
+	else
+		pr_info("File %s will be restored from fd %d duped "
+				"from inherit fd %d\n", id_str, *fd_p, i_fd);
+	return true;
+}
+
 /*
  * Look up the inherit fd list by a file descriptor.
  */

include/files.h

@@ -105,6 +105,7 @@ struct file_desc_ops {
 	 */
 	void			(*collect_fd)(struct file_desc *, struct fdinfo_list_entry *,
 						struct rst_info *);
+	char *			(*name)(struct file_desc *, char *b, size_t s);
 };
 
 static inline void collect_gen_fd(struct fdinfo_list_entry *fle, struct rst_info *ri)
@@ -170,8 +171,9 @@ extern int dump_unsupp_fd(struct fd_parms *p, int lfd,
 
 extern int inherit_fd_add(char *optarg);
 extern void inherit_fd_log(void);
-extern int inherit_fd_lookup_id(char *id);
 extern int inherit_fd_resolve_clash(int fd);
 extern int inherit_fd_fini(void);
 
+extern bool inherited_fd(struct file_desc *, int *fdp);
+
 #endif /* __CR_FILES_H__ */

pipes.c

@@ -293,48 +293,31 @@ static int recv_pipe_fd(struct pipe_info *pi)
 	return fd;
 }
 
-static char *pipe_id_string(int pipe_id)
+static char *pipe_d_name(struct file_desc *d, char *buf, size_t s)
 {
-	static char idstr[18];
+	struct pipe_info *pi;
 
-	if (snprintf(idstr, sizeof idstr, "pipe:[%d]", pipe_id) >= sizeof idstr) {
-		pr_err("Not enough room for pipe %d identifier string\n", pipe_id);
+	pi = container_of(d, struct pipe_info, d);
+	if (snprintf(buf, s, "pipe:[%d]", pi->pe->pipe_id) >= s) {
+		pr_err("Not enough room for pipe %d identifier string\n",
+				pi->pe->pipe_id);
 		return NULL;
 	}
-	return idstr;
+
+	return buf;
 }
 
 static int open_pipe(struct file_desc *d)
 {
-	char *pipe_name;
 	struct pipe_info *pi, *p;
 	int ret, tmp;
 	int pfd[2];
 	int sock;
 
-	pi = container_of(d, struct pipe_info, d);
-
-	/*
-	 * If the pipe is in the inherit fd list,
-	 * it should be inherited rather than created.
-	 */
-	pipe_name = pipe_id_string(pi->pe->pipe_id);
-	if (pipe_name == NULL)
-		return -1;
-	tmp = inherit_fd_lookup_id(pipe_name);
-	if (tmp >= 0) {
-		int fd;
-
-		fd = dup(tmp);
-		if (fd == -1) {
-			pr_perror("Can't dup inherit fd %d\n", fd);
-			return -1;
-		}
-		pr_info("Pipe %s will be restored from fd %d duped from inherit fd %d\n",
-			pipe_name, fd, tmp);
-		return fd;
-	}
+	if (inherited_fd(d, &tmp))
+		return tmp;
 
+	pi = container_of(d, struct pipe_info, d);
 	pr_info("\t\tCreating pipe pipe_id=%#x id=%#x\n", pi->pe->pipe_id, pi->pe->id);
 
 	if (!pi->create)
@@ -396,6 +379,7 @@ static struct file_desc_ops pipe_desc_ops = {
 	.type		= FD_TYPES__PIPE,
 	.open		= open_pipe,
 	.want_transport	= want_transport,
+	.name		= pipe_d_name,
 };
 
 static int collect_one_pipe(void *o, ProtobufCMessage *base)