stand: add fs_ops.fs_flag

To avoid a layering violation in open() allow fs_ops to
indicate that devopen() should be skipped.

This is only true for pkgfs.

Sponsored by:	Juniper Networks, Inc.
Differential Revision:	https://reviews.freebsd.org/D51684

Author: sgerraty

stand/libsa/bzipfs.c

@@ -68,6 +68,7 @@ static int	bzf_stat(struct open_file *f, struct stat *sb);
 #ifndef REGRESSION
 struct fs_ops bzipfs_fsops = {
 	.fs_name = "bzip",
+	.fs_flags = 0,
 	.fo_open = bzf_open,
 	.fo_close = bzf_close,
 	.fo_read = bzf_read,

stand/libsa/cd9660.c

@@ -81,6 +81,7 @@ static ISO_SUSP_HEADER *susp_lookup_record(struct open_file *f,
 
 struct fs_ops cd9660_fsops = {
 	.fs_name = "cd9660",
+	.fs_flags = 0,
 	.fo_open = cd9660_open,
 	.fo_close = cd9660_close,
 	.fo_read = cd9660_read,

stand/libsa/dosfs.c

@@ -61,6 +61,7 @@ static int	dos_unmount(const char *dev, void *data);
 
 struct fs_ops dosfs_fsops = {
 	.fs_name = "dosfs",
+	.fs_flags = 0,
 	.fo_open = dos_open,
 	.fo_close = dos_close,
 	.fo_read = dos_read,

stand/libsa/ext2fs.c

@@ -106,6 +106,7 @@ static int dtmap[] = { DT_UNKNOWN, DT_REG, DT_DIR, DT_CHR,
 
 struct fs_ops ext2fs_fsops = {
 	.fs_name = "ext2fs",
+	.fs_flags = 0,
 	.fo_open = ext2fs_open,
 	.fo_close = ext2fs_close,
 	.fo_read = ext2fs_read,

stand/libsa/gzipfs.c

@@ -50,6 +50,7 @@ static int	zf_stat(struct open_file *f, struct stat *sb);
 
 struct fs_ops gzipfs_fsops = {
 	.fs_name = "zip",
+	.fs_flags = 0,
 	.fo_open = zf_open,
 	.fo_close = zf_close,
 	.fo_read = zf_read,

stand/libsa/nfs.c

@@ -131,6 +131,7 @@ struct	nfs_iodesc nfs_root_node;
 
 struct fs_ops nfs_fsops = {
 	.fs_name = "nfs",
+	.fs_flags = 0,
 	.fo_open = nfs_open,
 	.fo_close = nfs_close,
 	.fo_read = nfs_read,

stand/libsa/open.c

@@ -154,27 +154,32 @@ open(const char *fname, int mode)
 	f->f_devdata = NULL;
 	file = NULL;
 
+	if (exclusive_file_system == NULL ||
+	    (exclusive_file_system->fs_flags & FS_OPS_NO_DEVOPEN) == 0) {
+		error = devopen(f, fname, &file);
+		if (error ||
+		    (((f->f_flags & F_NODEV) == 0) && f->f_dev == NULL))
+			goto err;
+
+		/* see if we opened a raw device; otherwise, 'file' is the file name. */
+		if (file == NULL || *file == '\0') {
+			f->f_flags |= F_RAW;
+			f->f_rabuf = NULL;
+			TSEXIT();
+			return (fd);
+		}
+	} else
+		file = fname;
+
 	if (exclusive_file_system != NULL) {
+		/* loader is forcing the filesystem to be used */
 		fs = exclusive_file_system;
-		error = (fs->fo_open)(fname, f);
+		error = (fs->fo_open)(file, f);
 		if (error == 0)
 			goto ok;
 		goto err;
 	}
 
-	error = devopen(f, fname, &file);
-	if (error ||
-	    (((f->f_flags & F_NODEV) == 0) && f->f_dev == NULL))
-		goto err;
-
-	/* see if we opened a raw device; otherwise, 'file' is the file name. */
-	if (file == NULL || *file == '\0') {
-		f->f_flags |= F_RAW;
-		f->f_rabuf = NULL;
-		TSEXIT();
-		return (fd);
-	}
-
 	/* pass file name to the different filesystem open routines */
 	besterror = ENOENT;
 	for (i = 0; file_system[i] != NULL; i++) {

stand/libsa/pkgfs.c

@@ -41,6 +41,7 @@ static off_t pkg_atol(const char *, unsigned);
 
 struct fs_ops pkgfs_fsops = {
 	.fs_name = "pkg",
+	.fs_flags = FS_OPS_NO_DEVOPEN,
 	.fo_open = pkg_open,
 	.fo_close = pkg_close,
 	.fo_read = pkg_read,

stand/libsa/splitfs.c

@@ -50,6 +50,7 @@ static int	splitfs_stat(struct open_file *f, struct stat *sb);
 
 struct fs_ops splitfs_fsops = {
 	.fs_name = "split",
+	.fs_flags = 0,
 	.fo_open = splitfs_open,
 	.fo_close = splitfs_close,
 	.fo_read = splitfs_read,

stand/libsa/stand.h

@@ -94,6 +94,8 @@ __BEGIN_DECLS
 
 struct open_file;
 
+#define FS_OPS_NO_DEVOPEN 1
+
 /*
  * This structure is used to define file system operations in a file system
  * independent way.
@@ -104,6 +106,7 @@ struct open_file;
  */
 struct fs_ops {
     const char	*fs_name;
+    int		fs_flags;
     int		(*fo_open)(const char *path, struct open_file *f);
     int		(*fo_close)(struct open_file *f);
     int		(*fo_read)(struct open_file *f, void *buf,