[RFC PATCH 1/6] Implement reexport helper library

[Richard Weinberger <richard@nod.at>]

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  | 477 +++++++++++++++++++++++++++++++++++
 support/reexport/reexport.h  |  53 ++++
 5 files changed, 552 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" = "yes" ])
 
+AC_ARG_ENABLE(reexport,
+	[AC_HELP_STRING([--enable-reexport],
+			[enable support for re-exporting NFS mounts  @<:@default=no@:>@])],
+	enable_reexport=$enableval,
+	enable_reexport="no")
+	if test "$enable_reexport" = 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" = "yes" ])
+
 dnl Check for TI-RPC library and headers
 AC_LIBTIRPC
 
@@ -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 += junction
 endif
 
+if CONFIG_REEXPORT
+OPTDIRS += reexport
+endif
+
 SUBDIRS = export include misc nfs nsm $(OPTDIRS)
 
 MAINTAINERCLEANFILES = 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 = libreexport.a
+libreexport_a_SOURCES = reexport.c
+
+MAINTAINERCLEANFILES = Makefile.in
diff --git a/support/reexport/reexport.c b/support/reexport/reexport.c
new file mode 100644
index 00000000..551ec278
--- /dev/null
+++ b/support/reexport/reexport.c
@@ -0,0 +1,477 @@
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <sqlite3.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <sys/file.h>
+#include <sys/mman.h>
+#include <sys/shm.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/vfs.h>
+#include <unistd.h>
+
+#include "nfslib.h"
+#include "reexport.h"
+#include "xlog.h"
+
+#define REEXPDB_SHM_NAME "/nfs_reexport_db_lock"
+#define REEXPDB_SHM_SZ 4096
+#define REEXPDB_INIT_LOCK NFS_STATEDIR "/reexpdb_init.lock"
+#define REEXPDB_DBFILE NFS_STATEDIR "/reexpdb.sqlite3"
+
+static const char initdb_sql[] = "CREATE TABLE IF NOT EXISTS fsidnums (num INTEGER PRIMARY KEY CHECK (num > 0 AND num < 4294967296), path TEXT UNIQUE); CREATE TABLE IF NOT EXISTS subvolumes (path TEXT PRIMARY KEY); CREATE INDEX IF NOT EXISTS idx_ids_path ON fsidnums (path);";
+/*
+ * This query is a little tricky. We use SQL to find and claim the smallest free fsid number.
+ * To find a free fsid the fsidnums is left joined to itself but with an offset of 1.
+ * Everything after the UNION statement is to handle the corner case where fsidnums
+ * is empty. In this case we want 1 as first fsid number.
+ */
+static const char new_fsidnum_by_path_sql[] = "INSERT INTO fsidnums VALUES ((SELECT ids1.num + 1 FROM fsidnums AS ids1 LEFT JOIN fsidnums AS ids2 ON ids2.num = ids1.num + 1 WHERE ids2.num IS NULL UNION SELECT 1 WHERE NOT EXISTS (SELECT NULL FROM fsidnums WHERE num = 1) LIMIT 1), ?1) RETURNING num;";
+static const char fsidnum_by_path_sql[] = "SELECT num FROM fsidnums WHERE path = ?1;";
+static const char add_crossed_volume_sql[] = "REPLACE INTO subvolumes VALUES(?1);";
+static const char drop_crossed_volume_sql[] = "DELETE FROM subvolumes WHERE path = ?1;";
+static const char get_crossed_volumes_sql[] = "SELECT path from subvolumes;";
+
+static sqlite3 *db;
+static pthread_rwlock_t *reexpdb_rwlock;
+static int init_done;
+
+static void reexpdb_wrlock(void)
+{
+	assert(pthread_rwlock_wrlock(reexpdb_rwlock) == 0);
+}
+
+static void reexpdb_rdlock(void)
+{
+	assert(pthread_rwlock_rdlock(reexpdb_rwlock) == 0);
+}
+
+static void reexpdb_unlock(void)
+{
+	assert(pthread_rwlock_unlock(reexpdb_rwlock) == 0);
+}
+
+static int init_shm_lock(void)
+{
+	int lockfd = -1, shmfd = -1;
+	int initlock = 0;
+	int ret = 0;
+
+	assert(sizeof(*reexpdb_rwlock) <= REEXPDB_SHM_SZ);
+
+	lockfd = open(REEXPDB_INIT_LOCK, O_RDWR | O_CREAT, 0600);
+	if (lockfd == -1) {
+		ret = -1;
+		xlog(L_FATAL, "Unable to open %s: %m", REEXPDB_INIT_LOCK);
+
+		goto out;
+	}
+
+	ret = flock(lockfd, LOCK_EX);
+	if (ret == -1) {
+		ret = -1;
+		xlog(L_FATAL, "Unable to lock %s: %m", REEXPDB_INIT_LOCK);
+
+		goto out_close;
+	}
+
+	shmfd = shm_open(REEXPDB_SHM_NAME, O_RDWR, 0600);
+	if (shmfd == -1 && errno == ENOENT) {
+		shmfd = shm_open(REEXPDB_SHM_NAME, O_RDWR | O_CREAT, 0600);
+		if (shmfd == -1) {
+			ret = -1;
+			xlog(L_FATAL, "Unable to create shared memory: %m");
+			goto out_unflock;
+		}
+
+		ret = ftruncate(shmfd, REEXPDB_SHM_SZ);
+		if (ret == -1) {
+			ret = -1;
+			xlog(L_FATAL, "Unable to ftruncate shared memory: %m");
+			goto out_unflock;
+		}
+
+		initlock = 1;
+	} else if (shmfd == -1) {
+		ret = -1;
+		xlog(L_FATAL, "Unable to open shared memory: %m");
+		goto out_unflock;
+	}
+
+        reexpdb_rwlock = mmap(NULL, REEXPDB_SHM_SZ, PROT_READ | PROT_WRITE, MAP_SHARED, shmfd, 0);
+	close(shmfd);
+        if (reexpdb_rwlock == (void *)-1) {
+                xlog(L_FATAL, "Unable to mmap shared memory: %m");
+		ret = -1;
+		goto out_unflock;
+        }
+
+	if (initlock) {
+		pthread_rwlockattr_t attr;
+
+		ret = pthread_rwlockattr_init(&attr);
+		if (ret != 0) {
+			xlog(L_FATAL, "Unable to pthread_rwlockattr_init: %m");
+			ret = -1;
+			goto out_unflock;
+		}
+
+		ret = pthread_rwlockattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
+		if (ret != 0) {
+			xlog(L_FATAL, "Unable to set PTHREAD_PROCESS_SHARED: %m");
+			ret = -1;
+			goto out_unflock;
+		}
+
+		ret = pthread_rwlock_init(reexpdb_rwlock, &attr);
+		if (ret != 0) {
+			xlog(L_FATAL, "Unable to pthread_rwlock_init: %m");
+			ret = -1;
+			goto out_unflock;
+		}
+	}
+
+	ret = 0;
+
+out_unflock:
+	flock(lockfd, LOCK_UN);
+out_close:
+	close(lockfd);
+out:
+	return ret;
+} 
+
+/*
+ * reexpdb_init - Initialize reexport database
+ *
+ * Setup shared lock (database is concurrently used by multiple processes),
+ * if needed create tables and create database handle.
+ * It is okay to call this function multiple times per process.
+ */
+int reexpdb_init(void)
+{
+	char *sqlerr;
+	int ret;
+
+	if (init_done)
+		return 0;
+
+	ret = init_shm_lock();
+	if (ret)
+		return -1;
+
+	ret = sqlite3_open_v2(REEXPDB_DBFILE, &db, SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE | SQLITE_OPEN_FULLMUTEX, NULL);
+	if (ret != SQLITE_OK) {
+		xlog(L_ERROR, "Unable to open reexport database: %s", sqlite3_errstr(ret));
+		return -1;
+	}
+
+	reexpdb_wrlock();
+	ret = sqlite3_exec(db, initdb_sql, NULL, NULL, &sqlerr);
+	reexpdb_unlock();
+	if (ret != SQLITE_OK) {
+		xlog(L_ERROR, "Unable to init reexport database: %s", sqlite3_errstr(ret));
+		sqlite3_free(sqlerr);
+		sqlite3_close_v2(db);
+		ret = -1;
+	} else {
+		init_done = 1;
+		ret = 0;
+	}
+
+	return ret;
+}
+
+/*
+ * reexpdb_destroy - Undo reexpdb_init().
+ *
+ * The shared lock keeps. We cannot know which other
+ * processes are still use the database.
+ */
+void reexpdb_destroy(void)
+{
+	if (!init_done)
+		return;
+
+	sqlite3_close_v2(db);
+	munmap((void *)reexpdb_rwlock, REEXPDB_SHM_SZ);
+	reexpdb_rwlock = NULL;
+}
+
+static int get_fsidnum_by_path(char *path, uint32_t *fsidnum)
+{
+	sqlite3_stmt *stmt = NULL;
+	int found = 0;
+	int ret;
+
+	ret = sqlite3_prepare_v2(db, fsidnum_by_path_sql, sizeof(fsidnum_by_path_sql), &stmt, NULL);
+	if (ret != SQLITE_OK) {
+		xlog(L_WARNING, "Unable to prepare SQL query: %s", sqlite3_errstr(ret));
+		goto out;
+	}
+
+	ret = sqlite3_bind_text(stmt, 1, path, -1, NULL);
+	if (ret != SQLITE_OK) {
+		xlog(L_WARNING, "Unable to bind \"%s\" SQL query: %s", __func__, sqlite3_errstr(ret));
+		goto out;
+	}
+
+	reexpdb_rdlock();
+	ret = sqlite3_step(stmt);
+	if (ret == SQLITE_ROW) {
+		*fsidnum = sqlite3_column_int(stmt, 0);
+		found = 1;
+	} else if (ret == SQLITE_DONE) {
+		/* No hit */
+		found = 0;
+	} else {
+		xlog(L_WARNING, "Error while looking up \"%s\" in database: %s", path, sqlite3_errstr(ret));
+	}
+	reexpdb_unlock();
+
+out:
+	sqlite3_finalize(stmt);
+	return found;
+}
+
+static int new_fsidnum_by_path(char *path, uint32_t *fsidnum)
+{
+	sqlite3_stmt *stmt = NULL;
+	int found = 0, check = 0;
+	int ret;
+
+	ret = sqlite3_prepare_v2(db, new_fsidnum_by_path_sql, sizeof(new_fsidnum_by_path_sql), &stmt, NULL);
+	if (ret != SQLITE_OK) {
+		xlog(L_WARNING, "Unable to prepare SQL query: %s", sqlite3_errstr(ret));
+		goto out;
+	}
+
+	ret = sqlite3_bind_text(stmt, 1, path, -1, NULL);
+	if (ret != SQLITE_OK) {
+		xlog(L_WARNING, "Unable to bind \"%s\" SQL query: %s", path, sqlite3_errstr(ret));
+		goto out;
+	}
+
+	reexpdb_wrlock();
+	ret = sqlite3_step(stmt);
+	if (ret == SQLITE_ROW) {
+		*fsidnum = sqlite3_column_int(stmt, 0);
+		found = 1;
+	} else if (ret == SQLITE_CONSTRAINT) {
+		/* Maybe we lost the race against another writer and the path is now present. */
+		check = 1;
+	} else {
+		xlog(L_WARNING, "Error while looking up \"%s\" in database: %s", path, sqlite3_errstr(ret));
+	}
+	reexpdb_unlock();
+
+out:
+	sqlite3_finalize(stmt);
+
+	if (check) {
+		found = get_fsidnum_by_path(path, fsidnum);
+		if (!found)
+			xlog(L_WARNING, "SQLITE_CONSTRAINT error while inserting \"%s\" in database", path);
+	}
+
+	return found;
+}
+
+int reexpdb_fsidnum_by_path(char *path, uint32_t *fsidnum, int may_create)
+{
+	int found;
+
+	found = get_fsidnum_by_path(path, fsidnum);
+
+	if (!found && may_create)
+		found = new_fsidnum_by_path(path, fsidnum);
+
+	return found;
+}
+
+int reexpdb_apply_reexport_settings(struct exportent *ep, char *flname, int flline)
+{
+	int ret = 0;
+
+	switch (ep->e_reexport) {
+	case REEXP_REMOTE_DEVFSID:
+		if (!ep->e_fsid && !ep->e_uuid) {
+			xlog(L_ERROR, "%s:%i: Selected 'reexport=' mode needs either a numerical or UUID 'fsid='\n",
+			     flname, flline);
+			ret = -1;
+		}
+		break;
+	case REEXP_AUTO_FSIDNUM:
+	case REEXP_PREDEFINED_FSIDNUM: {
+		uint32_t fsidnum;
+		int found;
+
+		if (ep->e_uuid)
+			break;
+
+		if (reexpdb_init() != 0) {
+			ret = -1;
+
+			break;
+		}
+
+		found = reexpdb_fsidnum_by_path(ep->e_path, &fsidnum, 0);
+		if (!found) {
+			if (ep->e_reexport == REEXP_AUTO_FSIDNUM) {
+				found = reexpdb_fsidnum_by_path(ep->e_path, &fsidnum, 1);
+				if (!found) {
+					xlog(L_ERROR, "%s:%i: Unable to generate fsid for %s",
+					     flname, flline, ep->e_path);
+					ret = -1;
+
+					break;
+				}
+			} else {
+				if (!ep->e_fsid) {
+					xlog(L_ERROR, "%s:%i: Selected 'reexport=' mode requires either a UUID 'fsid=' or a numerical 'fsid=' or a reexport db entry %d",
+					     flname, flline, ep->e_fsid);
+					ret = -1;
+				}
+
+				break;
+			}
+		}
+
+		if (ep->e_fsid) {
+			if (ep->e_fsid != fsidnum) {
+				xlog(L_ERROR, "%s:%i: Selected 'reexport=' mode requires configured numerical 'fsid=' to agree with reexport db entry",
+				     flname, flline);
+				ret = -1;
+			}
+
+			break;
+		}
+
+		ep->e_fsid = fsidnum;
+
+		break;
+	}
+	}
+
+	return ret;
+}
+
+int reexpdb_add_subvolume(char *path)
+{
+	sqlite3_stmt *stmt = NULL;
+	int ret;
+
+	reexpdb_wrlock();
+	ret = sqlite3_prepare_v2(db, add_crossed_volume_sql, sizeof(add_crossed_volume_sql), &stmt, NULL);
+	if (ret != SQLITE_OK) {
+		xlog(L_WARNING, "Unable to prepare SQL query: %s", sqlite3_errstr(ret));
+		ret = -1;
+		goto out;
+	}
+
+	ret = sqlite3_bind_text(stmt, 1, path, -1, NULL);
+	if (ret != SQLITE_OK) {
+		xlog(L_WARNING, "Unable to bind \"%s\" SQL query: %s", __func__, sqlite3_errstr(ret));
+		ret = -1;
+		goto out;
+	}
+
+	ret = sqlite3_step(stmt);
+	if (ret != SQLITE_DONE) {
+		xlog(L_WARNING, "Error while adding \"%s\" from database: %s", path, sqlite3_errstr(ret));
+		ret = -1;
+	} else {
+		ret = 0;
+	}
+
+out:
+	reexpdb_unlock();
+	sqlite3_finalize(stmt);
+	return ret;
+}
+
+int reexpdb_drop_subvolume_unlocked(char *path)
+{
+	sqlite3_stmt *stmt = NULL;
+	int ret;
+
+	ret = sqlite3_prepare_v2(db, drop_crossed_volume_sql, sizeof(drop_crossed_volume_sql), &stmt, NULL);
+	if (ret != SQLITE_OK) {
+		xlog(L_WARNING, "Unable to prepare SQL query: %s", sqlite3_errstr(ret));
+		ret = -1;
+		goto out;
+	}
+
+	ret = sqlite3_bind_text(stmt, 1, path, -1, NULL);
+	if (ret != SQLITE_OK) {
+		xlog(L_WARNING, "Unable to bind \"%s\" SQL query: %s", __func__, sqlite3_errstr(ret));
+		ret = -1;
+		goto out;
+	}
+
+	ret = sqlite3_step(stmt);
+	if (ret != SQLITE_DONE) {
+		xlog(L_WARNING, "Error while deleting \"%s\" from database: %s", path, sqlite3_errstr(ret));
+		ret = -1;
+	} else {
+		ret = 0;
+	}
+
+out:
+	sqlite3_finalize(stmt);
+	return ret;
+}
+
+
+int reexpdb_uncover_subvolumes(void (*cb)(char *path))
+{
+	sqlite3_stmt *stmt = NULL;
+	struct statfs st;
+	const unsigned char *path;
+	int ret;
+
+	if (cb)
+		reexpdb_wrlock();
+	else
+		reexpdb_rdlock();
+
+	ret = sqlite3_prepare_v2(db, get_crossed_volumes_sql, sizeof(get_crossed_volumes_sql), &stmt, NULL);
+	if (ret != SQLITE_OK) {
+		xlog(L_WARNING, "Unable to prepare SQL query: %s", sqlite3_errstr(ret));
+		ret = -1;
+		goto out;
+	}
+
+	for (;;) {
+		ret = sqlite3_step(stmt);
+		if (ret != SQLITE_ROW)
+			break;
+
+		path = sqlite3_column_text(stmt, 0);
+		if (cb)
+			cb((char *)path);
+		else
+			statfs((char *)path, &st);
+	}
+
+	if (ret != SQLITE_DONE) {
+		xlog(L_WARNING, "Error while reading all subvolumes: %s", sqlite3_errstr(ret));
+		ret = -1;
+		goto out_unlock;
+	}
+
+	ret = 0;
+
+out_unlock:
+	reexpdb_unlock();
+	sqlite3_finalize(stmt);
+out:
+	return ret;
+}
diff --git a/support/reexport/reexport.h b/support/reexport/reexport.h
new file mode 100644
index 00000000..46ec8a96
--- /dev/null
+++ b/support/reexport/reexport.h
@@ -0,0 +1,53 @@
+#ifndef REEXPORT_H
+#define REEXPORT_H
+
+enum {
+	REEXP_NONE = 0,
+	REEXP_AUTO_FSIDNUM,
+	REEXP_PREDEFINED_FSIDNUM,
+	REEXP_REMOTE_DEVFSID,
+};
+
+#ifdef HAVE_REEXPORT_SUPPORT
+int reexpdb_init(void);
+void reexpdb_destroy(void);
+int reexpdb_fsidnum_by_path(char *path, uint32_t *fsidnum, int may_create);
+int reexpdb_apply_reexport_settings(struct exportent *ep, char *flname, int flline);
+int reexpdb_add_subvolume(char *path);
+int reexpdb_uncover_subvolumes(void (*cb)(char *path));
+int reexpdb_drop_subvolume_unlocked(char *path);
+#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 = 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 int reexpdb_add_subvolume(char *path)
+{
+	(void)path;
+	return 0;
+}
+static inline int reexpdb_uncover_subvolumes(void (*cb)(char *path))
+{
+	(void)cb;
+	return 0;
+}
+static inline int reexpdb_drop_subvolume_unlocked(char *path)
+{
+	(void)path;
+	return 0;
+}
+#endif /* HAVE_REEXPORT_SUPPORT */
+
+#endif /* REEXPORT_H */
-- 
2.31.1