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From:   Richard Weinberger <richard@nod.at>
To:     linux-nfs@vger.kernel.org
Cc:     david@sigma-star.at, bfields@fieldses.org,
        luis.turcitu@appsbroker.com, david.young@appsbroker.com,
        david.oberhollenzer@sigma-star.at, trond.myklebust@hammerspace.com,
        anna.schumaker@netapp.com, steved@redhat.com,
        chris.chilvers@appsbroker.com, Richard Weinberger <richard@nod.at>
Subject: [PATCH 1/5] Implement reexport helper library
Date:   Mon,  2 May 2022 10:50:41 +0200
Message-Id: <20220502085045.13038-2-richard@nod.at>
In-Reply-To: <20220502085045.13038-1-richard@nod.at>
References: <20220502085045.13038-1-richard@nod.at>
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

This internal library contains code that will be used by various
tools within the nfs-utils package to deal better with NFS re-export,
especially cross mounts.

Signed-off-by: Richard Weinberger <richard@nod.at>
---
 configure.ac                 |  12 ++
 support/Makefile.am          |   4 +
 support/reexport/Makefile.am |   6 +
 support/reexport/reexport.c  | 285 +++++++++++++++++++++++++++++++++++
 support/reexport/reexport.h  |  39 +++++
 5 files changed, 346 insertions(+)
 create mode 100644 support/reexport/Makefile.am
 create mode 100644 support/reexport/reexport.c
 create mode 100644 support/reexport/reexport.h

diff --git a/configure.ac b/configure.ac
index 93626d62..86bf8ba9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -274,6 +274,17 @@ AC_ARG_ENABLE(nfsv4server,
 	fi
 	AM_CONDITIONAL(CONFIG_NFSV4SERVER, [test "$enable_nfsv4server" =3D "yes=
" ])
=20
+AC_ARG_ENABLE(reexport,
+	[AC_HELP_STRING([--enable-reexport],
+			[enable support for re-exporting NFS mounts  @<:@default=3Dno@:>@])],
+	enable_reexport=3D$enableval,
+	enable_reexport=3D"no")
+	if test "$enable_reexport" =3D yes; then
+		AC_DEFINE(HAVE_REEXPORT_SUPPORT, 1,
+                          [Define this if you want NFS re-export support=
 compiled in])
+	fi
+	AM_CONDITIONAL(CONFIG_REEXPORT, [test "$enable_reexport" =3D "yes" ])
+
 dnl Check for TI-RPC library and headers
 AC_LIBTIRPC
=20
@@ -730,6 +741,7 @@ AC_CONFIG_FILES([
 	support/nsm/Makefile
 	support/nfsidmap/Makefile
 	support/nfsidmap/libnfsidmap.pc
+	support/reexport/Makefile
 	tools/Makefile
 	tools/locktest/Makefile
 	tools/nlmtest/Makefile
diff --git a/support/Makefile.am b/support/Makefile.am
index c962d4d4..986e9b5f 100644
--- a/support/Makefile.am
+++ b/support/Makefile.am
@@ -10,6 +10,10 @@ if CONFIG_JUNCTION
 OPTDIRS +=3D junction
 endif
=20
+if CONFIG_REEXPORT
+OPTDIRS +=3D reexport
+endif
+
 SUBDIRS =3D export include misc nfs nsm $(OPTDIRS)
=20
 MAINTAINERCLEANFILES =3D Makefile.in
diff --git a/support/reexport/Makefile.am b/support/reexport/Makefile.am
new file mode 100644
index 00000000..9d544a8f
--- /dev/null
+++ b/support/reexport/Makefile.am
@@ -0,0 +1,6 @@
+## Process this file with automake to produce Makefile.in
+
+noinst_LIBRARIES =3D libreexport.a
+libreexport_a_SOURCES =3D reexport.c
+
+MAINTAINERCLEANFILES =3D Makefile.in
diff --git a/support/reexport/reexport.c b/support/reexport/reexport.c
new file mode 100644
index 00000000..5474a21f
--- /dev/null
+++ b/support/reexport/reexport.c
@@ -0,0 +1,285 @@
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <sqlite3.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <sys/random.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/vfs.h>
+#include <unistd.h>
+
+#include "nfsd_path.h"
+#include "nfslib.h"
+#include "reexport.h"
+#include "xcommon.h"
+#include "xlog.h"
+
+#define REEXPDB_DBFILE NFS_STATEDIR "/reexpdb.sqlite3"
+#define REEXPDB_DBFILE_WAIT_USEC (5000)
+
+static sqlite3 *db;
+static int init_done;
+
+static int prng_init(void)
+{
+	int seed;
+
+	if (getrandom(&seed, sizeof(seed), 0) !=3D sizeof(seed)) {
+		xlog(L_ERROR, "Unable to obtain seed for PRNG via getrandom()");
+		return -1;
+	}
+
+	srand(seed);
+	return 0;
+}
+
+static void wait_for_dbaccess(void)
+{
+	usleep(REEXPDB_DBFILE_WAIT_USEC + (rand() % REEXPDB_DBFILE_WAIT_USEC));
+}
+
+/*
+ * reexpdb_init - Initialize reexport database
+ */
+int reexpdb_init(void)
+{
+	char *sqlerr;
+	int ret;
+
+	if (init_done)
+		return 0;
+
+	if (prng_init() !=3D 0)
+		return -1;
+
+	ret =3D sqlite3_open_v2(REEXPDB_DBFILE, &db, SQLITE_OPEN_READWRITE | SQ=
LITE_OPEN_CREATE | SQLITE_OPEN_FULLMUTEX, NULL);
+	if (ret !=3D SQLITE_OK) {
+		xlog(L_ERROR, "Unable to open reexport database: %s", sqlite3_errstr(r=
et));
+		return -1;
+	}
+
+again:
+	ret =3D sqlite3_exec(db, "CREATE TABLE IF NOT EXISTS fsidnums (num INTE=
GER PRIMARY KEY CHECK (num > 0 AND num < 4294967296), path TEXT UNIQUE); =
CREATE INDEX IF NOT EXISTS idx_ids_path ON fsidnums (path);", NULL, NULL,=
 &sqlerr);
+	switch (ret) {
+	case SQLITE_OK:
+		init_done =3D 1;
+		ret =3D 0;
+		break;
+	case SQLITE_BUSY:
+	case SQLITE_LOCKED:
+		wait_for_dbaccess();
+		goto again;
+	default:
+		xlog(L_ERROR, "Unable to init reexport database: %s", sqlite3_errstr(r=
et));
+		sqlite3_free(sqlerr);
+		sqlite3_close_v2(db);
+		ret =3D -1;
+	}
+
+	return ret;
+}
+
+/*
+ * reexpdb_destroy - Undo reexpdb_init().
+ */
+void reexpdb_destroy(void)
+{
+	if (!init_done)
+		return;
+
+	sqlite3_close_v2(db);
+}
+
+static int get_fsidnum_by_path(char *path, uint32_t *fsidnum)
+{
+	static const char fsidnum_by_path_sql[] =3D "SELECT num FROM fsidnums W=
HERE path =3D ?1;";
+	sqlite3_stmt *stmt =3D NULL;
+	int found =3D 0;
+	int ret;
+
+	ret =3D sqlite3_prepare_v2(db, fsidnum_by_path_sql, sizeof(fsidnum_by_p=
ath_sql), &stmt, NULL);
+	if (ret !=3D SQLITE_OK) {
+		xlog(L_WARNING, "Unable to prepare SQL query '%s': %s", fsidnum_by_pat=
h_sql, sqlite3_errstr(ret));
+		goto out;
+	}
+
+	ret =3D sqlite3_bind_text(stmt, 1, path, -1, NULL);
+	if (ret !=3D SQLITE_OK) {
+		xlog(L_WARNING, "Unable to bind SQL query '%s': %s", fsidnum_by_path_s=
ql, sqlite3_errstr(ret));
+		goto out;
+	}
+
+again:
+	ret =3D sqlite3_step(stmt);
+	switch (ret) {
+	case SQLITE_ROW:
+		*fsidnum =3D sqlite3_column_int(stmt, 0);
+		found =3D 1;
+		break;
+	case SQLITE_DONE:
+		/* No hit */
+		found =3D 0;
+		break;
+	case SQLITE_BUSY:
+	case SQLITE_LOCKED:
+		wait_for_dbaccess();
+		goto again;
+	default:
+		xlog(L_WARNING, "Error while looking up '%s' in database: %s", path, s=
qlite3_errstr(ret));
+	}
+
+out:
+	sqlite3_finalize(stmt);
+	return found;
+}
+
+static int get_path_by_fsidnum(uint32_t fsidnum, char **path)
+{
+	static const char path_by_fsidnum_sql[] =3D "SELECT path FROM fsidnums =
WHERE num =3D ?1;";
+	sqlite3_stmt *stmt =3D NULL;
+	int found =3D 0;
+	int ret;
+
+	ret =3D sqlite3_prepare_v2(db, path_by_fsidnum_sql, sizeof(path_by_fsid=
num_sql), &stmt, NULL);
+	if (ret !=3D SQLITE_OK) {
+		xlog(L_WARNING, "Unable to prepare SQL query '%s': %s", path_by_fsidnu=
m_sql, sqlite3_errstr(ret));
+		goto out;
+	}
+
+	ret =3D sqlite3_bind_int(stmt, 1, fsidnum);
+	if (ret !=3D SQLITE_OK) {
+		xlog(L_WARNING, "Unable to bind SQL query '%s': %s", path_by_fsidnum_s=
ql, sqlite3_errstr(ret));
+		goto out;
+	}
+
+again:
+	ret =3D sqlite3_step(stmt);
+	switch (ret) {
+	case SQLITE_ROW:
+		*path =3D xstrdup((char *)sqlite3_column_text(stmt, 0));
+		found =3D 1;
+		break;
+	case SQLITE_DONE:
+		/* No hit */
+		found =3D 0;
+		break;
+	case SQLITE_BUSY:
+	case SQLITE_LOCKED:
+		wait_for_dbaccess();
+		goto again;
+	default:
+		xlog(L_WARNING, "Error while looking up '%i' in database: %s", fsidnum=
, sqlite3_errstr(ret));
+	}
+
+out:
+	sqlite3_finalize(stmt);
+	return found;
+}
+
+static int new_fsidnum_by_path(char *path, uint32_t *fsidnum)
+{
+	/*
+	 * This query is a little tricky. We use SQL to find and claim the smal=
lest free fsid number.
+	 * To find a free fsid the fsidnums is left joined to itself but with a=
n offset of 1.
+	 * Everything after the UNION statement is to handle the corner case wh=
ere fsidnums
+	 * is empty. In this case we want 1 as first fsid number.
+	 */
+	static const char new_fsidnum_by_path_sql[] =3D "INSERT INTO fsidnums V=
ALUES ((SELECT ids1.num + 1 FROM fsidnums AS ids1 LEFT JOIN fsidnums AS i=
ds2 ON ids2.num =3D ids1.num + 1 WHERE ids2.num IS NULL UNION SELECT 1 WH=
ERE NOT EXISTS (SELECT NULL FROM fsidnums WHERE num =3D 1) LIMIT 1), ?1) =
RETURNING num;";
+
+	sqlite3_stmt *stmt =3D NULL;
+	int found =3D 0, check =3D 0;
+	int ret;
+
+	ret =3D sqlite3_prepare_v2(db, new_fsidnum_by_path_sql, sizeof(new_fsid=
num_by_path_sql), &stmt, NULL);
+	if (ret !=3D SQLITE_OK) {
+		xlog(L_WARNING, "Unable to prepare SQL query '%s': %s", new_fsidnum_by=
_path_sql, sqlite3_errstr(ret));
+		goto out;
+	}
+
+	ret =3D sqlite3_bind_text(stmt, 1, path, -1, NULL);
+	if (ret !=3D SQLITE_OK) {
+		xlog(L_WARNING, "Unable to bind SQL query '%s': %s", new_fsidnum_by_pa=
th_sql, sqlite3_errstr(ret));
+		goto out;
+	}
+
+again:
+	ret =3D sqlite3_step(stmt);
+	switch (ret) {
+	case SQLITE_ROW:
+		*fsidnum =3D sqlite3_column_int(stmt, 0);
+		found =3D 1;
+		break;
+	case SQLITE_CONSTRAINT:
+		/* Maybe we lost the race against another writer and the path is now p=
resent. */
+		check =3D 1;
+		break;
+	case SQLITE_BUSY:
+	case SQLITE_LOCKED:
+		wait_for_dbaccess();
+		goto again;
+	default:
+		xlog(L_WARNING, "Error while looking up '%s' in database: %s", path, s=
qlite3_errstr(ret));
+	}
+
+out:
+	sqlite3_finalize(stmt);
+
+	if (check) {
+		found =3D get_fsidnum_by_path(path, fsidnum);
+		if (!found)
+			xlog(L_WARNING, "SQLITE_CONSTRAINT error while inserting '%s' in data=
base", path);
+	}
+
+	return found;
+}
+
+/*
+ * reexpdb_fsidnum_by_path - Lookup a fsid by path.
+ *
+ * @path: File system path used as lookup key
+ * @fsidnum: Pointer where found fsid is written to
+ * @may_create: If non-zero, allocate new fsid if lookup failed
+ *
+ */
+int reexpdb_fsidnum_by_path(char *path, uint32_t *fsidnum, int may_creat=
e)
+{
+	int found;
+
+	found =3D get_fsidnum_by_path(path, fsidnum);
+
+	if (!found && may_create)
+		found =3D new_fsidnum_by_path(path, fsidnum);
+
+	return found;
+}
+
+/*
+ * reexpdb_uncover_subvolume - Make sure a subvolume is present.
+ *
+ * @fsidnum: Numerical fsid number to look for
+ *
+ * Subvolumes (NFS cross mounts) get automatically mounted upon first
+ * access and can vanish after fs.nfs.nfs_mountpoint_timeout seconds.
+ * Also if the NFS server reboots, clients can still have valid file
+ * handles for such a subvolume.
+ *
+ * If kNFSd asks mountd for the path of a given fsidnum it can
+ * trigger an automount by calling statfs() on the given path.
+ */
+void reexpdb_uncover_subvolume(uint32_t fsidnum)
+{
+	struct statfs64 st;
+	char *path =3D NULL;
+	int ret;
+
+	if (get_path_by_fsidnum(fsidnum, &path)) {
+		ret =3D nfsd_path_statfs64(path, &st);
+		if (ret =3D=3D -1)
+			xlog(L_WARNING, "statfs() failed");
+	}
+
+	free(path);
+}
diff --git a/support/reexport/reexport.h b/support/reexport/reexport.h
new file mode 100644
index 00000000..bb6d2a1b
--- /dev/null
+++ b/support/reexport/reexport.h
@@ -0,0 +1,39 @@
+#ifndef REEXPORT_H
+#define REEXPORT_H
+
+enum {
+	REEXP_NONE =3D 0,
+	REEXP_AUTO_FSIDNUM,
+	REEXP_PREDEFINED_FSIDNUM,
+};
+
+#ifdef HAVE_REEXPORT_SUPPORT
+int reexpdb_init(void);
+void reexpdb_destroy(void);
+int reexpdb_fsidnum_by_path(char *path, uint32_t *fsidnum, int may_creat=
e);
+int reexpdb_apply_reexport_settings(struct exportent *ep, char *flname, =
int flline);
+void reexpdb_uncover_subvolume(uint32_t fsidnum);
+#else
+static inline int reexpdb_init(void) { return 0; }
+static inline void reexpdb_destroy(void) {}
+static inline int reexpdb_fsidnum_by_path(char *path, uint32_t *fsidnum,=
 int may_create)
+{
+	(void)path;
+	(void)may_create;
+	*fsidnum =3D 0;
+	return 0;
+}
+static inline int reexpdb_apply_reexport_settings(struct exportent *ep, =
char *flname, int flline)
+{
+	(void)ep;
+	(void)flname;
+	(void)flline;
+	return 0;
+}
+static inline void reexpdb_uncover_subvolume(uint32_t fsidnum)
+{
+	(void)fsidnum;
+}
+#endif /* HAVE_REEXPORT_SUPPORT */
+
+#endif /* REEXPORT_H */
--=20
2.31.1