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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Steve Dickson <steved@redhat.com>
CC:     Richard Weinberger <richard@nod.at>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        david <david@sigma-star.at>, Bruce Fields <bfields@fieldses.org>,
        "luis.turcitu@appsbroker.com" <luis.turcitu@appsbroker.com>,
        "david.young@appsbroker.com" <david.young@appsbroker.com>,
        "david.oberhollenzer@sigma-star.at" 
        <david.oberhollenzer@sigma-star.at>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        "chris.chilvers@appsbroker.com" <chris.chilvers@appsbroker.com>
Subject: Re: [PATCH 1/5] Implement reexport helper library
Thread-Topic: [PATCH 1/5] Implement reexport helper library
Thread-Index: AQHYXgHgoneWG2g3iEC82B/y61YHaq0YKM4AgAAEiIA=
Date:   Tue, 10 May 2022 13:48:49 +0000
Message-ID: <1A6F1763-C95B-4678-B622-6D3300AF087E@oracle.com>
References: <20220502085045.13038-1-richard@nod.at>
 <20220502085045.13038-2-richard@nod.at>
 <f4ae288c-b7f3-25fe-ef08-7b37256771bb@redhat.com>
In-Reply-To: <f4ae288c-b7f3-25fe-ef08-7b37256771bb@redhat.com>
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> On May 10, 2022, at 9:32 AM, Steve Dickson <steved@redhat.com> wrote:
>=20
> Hello,
>=20
> 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 "$enable_nfsv4server" =3D "ye=
s" ])
>>  +AC_ARG_ENABLE(reexport,
>> +	[AC_HELP_STRING([--enable-reexport],
>> +			[enable support for re-exporting NFS mounts  @<:@default=3Dno@:>@])]=
,
>> +	enable_reexport=3D$enableval,
>> +	enable_reexport=3D"no")
>> +	if test "$enable_reexport" =3D yes; then
>> +		AC_DEFINE(HAVE_REEXPORT_SUPPORT, 1,
>> +                          [Define this if you want NFS re-export suppor=
t compiled in])
>> +	fi
>> +	AM_CONDITIONAL(CONFIG_REEXPORT, [test "$enable_reexport" =3D "yes" ])
>> +
> To get this moving I'm going to add a --disable-reexport flag

Hi Steve, no-one has given a reason why disabling support
for re-exports would be necessary. Therefore, can't this
switch just be removed?


> +AC_ARG_ENABLE(reexport,
> +       [AC_HELP_STRING([--disable-reexport],
> +                       [disable support for re-exporting NFS mounts @<:@=
default=3Dno@:>@])],
> +       enable_reexport=3D$enableval,
> +       enable_reexport=3D"yes")
> +       if test "$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=
" ])
> +
>=20
> steved.
>=20
>>  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 +=3D junction
>>  endif
>>  +if CONFIG_REEXPORT
>> +OPTDIRS +=3D reexport
>> +endif
>> +
>>  SUBDIRS =3D export include misc nfs nsm $(OPTDIRS)
>>    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 | S=
QLITE_OPEN_CREATE | SQLITE_OPEN_FULLMUTEX, NULL);
>> +	if (ret !=3D SQLITE_OK) {
>> +		xlog(L_ERROR, "Unable to open reexport database: %s", sqlite3_errstr(=
ret));
>> +		return -1;
>> +	}
>> +
>> +again:
>> +	ret =3D sqlite3_exec(db, "CREATE TABLE IF NOT EXISTS fsidnums (num INT=
EGER PRIMARY KEY CHECK (num > 0 AND num < 4294967296), path TEXT UNIQUE); C=
REATE INDEX IF NOT EXISTS idx_ids_path ON fsidnums (path);", NULL, NULL, &s=
qlerr);
>> +	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(=
ret));
>> +		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 =
WHERE 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_=
path_sql), &stmt, NULL);
>> +	if (ret !=3D SQLITE_OK) {
>> +		xlog(L_WARNING, "Unable to prepare SQL query '%s': %s", fsidnum_by_pa=
th_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_=
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_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, =
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[] =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_fsi=
dnum_sql), &stmt, NULL);
>> +	if (ret !=3D SQLITE_OK) {
>> +		xlog(L_WARNING, "Unable to prepare SQL query '%s': %s", path_by_fsidn=
um_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_=
sql, 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", fsidnu=
m, 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 sma=
llest 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 w=
here 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 =
VALUES ((SELECT ids1.num + 1 FROM fsidnums AS ids1 LEFT JOIN fsidnums AS id=
s2 ON ids2.num =3D ids1.num + 1 WHERE ids2.num IS NULL UNION SELECT 1 WHERE=
 NOT EXISTS (SELECT NULL FROM fsidnums WHERE num =3D 1) LIMIT 1), ?1) RETUR=
NING 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_fsi=
dnum_by_path_sql), &stmt, NULL);
>> +	if (ret !=3D SQLITE_OK) {
>> +		xlog(L_WARNING, "Unable to prepare SQL query '%s': %s", new_fsidnum_b=
y_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_p=
ath_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 =
present. */
>> +		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, =
sqlite3_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 dat=
abase", 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_crea=
te)
>> +{
>> +	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_crea=
te);
>> +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

--
Chuck Lever