Re: [PATCH 1/5] Implement reexport helper library

[Steve Dickson <steved@redhat.com>]

Hello,

On 5/2/22 4:50 AM, Richard Weinberger wrote:
> 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 "$enable_nfsv4server" = "yes" ])
>   
> +AC_ARG_ENABLE(reexport,
> +	[AC_HELP_STRING([--enable-reexport],
> +			[enable support for re-exporting NFS mounts  @<:@default=no@:>@])],
> +	enable_reexport=$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" ])
> +
To get this moving I'm going to add a --disable-reexport flag

+AC_ARG_ENABLE(reexport,
+       [AC_HELP_STRING([--disable-reexport],
+                       [disable support for re-exporting NFS mounts 
@<:@default=no@:>@])],
+       enable_reexport=$enableval,
+       enable_reexport="yes")
+       if test "$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" ])
+

steved.

>   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..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) != 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() != 0)
> +		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;
> +	}
> +
> +again:
> +	ret = sqlite3_exec(db, "CREATE TABLE IF NOT EXISTS fsidnums (num INTEGER 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 = 1;
> +		ret = 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(ret));
> +		sqlite3_free(sqlerr);
> +		sqlite3_close_v2(db);
> +		ret = -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[] = "SELECT num FROM fsidnums WHERE path = ?1;";
> +	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': %s", fsidnum_by_path_sql, sqlite3_errstr(ret));
> +		goto out;
> +	}
> +
> +	ret = sqlite3_bind_text(stmt, 1, path, -1, NULL);
> +	if (ret != SQLITE_OK) {
> +		xlog(L_WARNING, "Unable to bind SQL query '%s': %s", fsidnum_by_path_sql, sqlite3_errstr(ret));
> +		goto out;
> +	}
> +
> +again:
> +	ret = sqlite3_step(stmt);
> +	switch (ret) {
> +	case SQLITE_ROW:
> +		*fsidnum = sqlite3_column_int(stmt, 0);
> +		found = 1;
> +		break;
> +	case SQLITE_DONE:
> +		/* No hit */
> +		found = 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, sqlite3_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[] = "SELECT path FROM fsidnums WHERE num = ?1;";
> +	sqlite3_stmt *stmt = NULL;
> +	int found = 0;
> +	int ret;
> +
> +	ret = sqlite3_prepare_v2(db, path_by_fsidnum_sql, sizeof(path_by_fsidnum_sql), &stmt, NULL);
> +	if (ret != SQLITE_OK) {
> +		xlog(L_WARNING, "Unable to prepare SQL query '%s': %s", path_by_fsidnum_sql, sqlite3_errstr(ret));
> +		goto out;
> +	}
> +
> +	ret = sqlite3_bind_int(stmt, 1, fsidnum);
> +	if (ret != SQLITE_OK) {
> +		xlog(L_WARNING, "Unable to bind SQL query '%s': %s", path_by_fsidnum_sql, sqlite3_errstr(ret));
> +		goto out;
> +	}
> +
> +again:
> +	ret = sqlite3_step(stmt);
> +	switch (ret) {
> +	case SQLITE_ROW:
> +		*path = xstrdup((char *)sqlite3_column_text(stmt, 0));
> +		found = 1;
> +		break;
> +	case SQLITE_DONE:
> +		/* No hit */
> +		found = 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 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;";
> +
> +	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': %s", new_fsidnum_by_path_sql, sqlite3_errstr(ret));
> +		goto out;
> +	}
> +
> +	ret = sqlite3_bind_text(stmt, 1, path, -1, NULL);
> +	if (ret != SQLITE_OK) {
> +		xlog(L_WARNING, "Unable to bind SQL query '%s': %s", new_fsidnum_by_path_sql, sqlite3_errstr(ret));
> +		goto out;
> +	}
> +
> +again:
> +	ret = sqlite3_step(stmt);
> +	switch (ret) {
> +	case SQLITE_ROW:
> +		*fsidnum = sqlite3_column_int(stmt, 0);
> +		found = 1;
> +		break;
> +	case SQLITE_CONSTRAINT:
> +		/* Maybe we lost the race against another writer and the path is now present. */
> +		check = 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, sqlite3_errstr(ret));
> +	}
> +
> +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;
> +}
> +
> +/*
> + * 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_create)
> +{
> +	int found;
> +
> +	found = get_fsidnum_by_path(path, fsidnum);
> +
> +	if (!found && may_create)
> +		found = 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 = NULL;
> +	int ret;
> +
> +	if (get_path_by_fsidnum(fsidnum, &path)) {
> +		ret = nfsd_path_statfs64(path, &st);
> +		if (ret == -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 = 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_create);
> +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 = 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 */