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Message-ID: <8d8c0e43-5607-ca9b-d21e-b7599c5d7186@redhat.com>
Date:   Tue, 10 May 2022 16:08:00 -0400
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Subject: Re: [PATCH 1/5] Implement reexport helper library
Content-Language: en-US
To:     Chuck Lever III <chuck.lever@oracle.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>
References: <20220502085045.13038-1-richard@nod.at>
 <20220502085045.13038-2-richard@nod.at>
 <f4ae288c-b7f3-25fe-ef08-7b37256771bb@redhat.com>
 <1A6F1763-C95B-4678-B622-6D3300AF087E@oracle.com>
 <fe2ecc50-4036-2922-28d6-e2f139408961@redhat.com>
 <650BB9E2-7CBD-4A38-92AD-C2AC82DDBD8C@oracle.com>
From:   Steve Dickson <steved@redhat.com>
In-Reply-To: <650BB9E2-7CBD-4A38-92AD-C2AC82DDBD8C@oracle.com>
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Precedence: bulk


On 5/10/22 10:17 AM, Chuck Lever III wrote:
> 
> 
>> On May 10, 2022, at 10:04 AM, Steve Dickson <steved@redhat.com> wrote:
>>
>> Hey!
>>
>> On 5/10/22 9:48 AM, Chuck Lever III wrote:
>>>> On May 10, 2022, at 9:32 AM, Steve Dickson <steved@redhat.com> wrote:
>>>>
>>>> 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
>>> 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?
> 
>> The precedence has been that we used --disable-XXX flag
>> a lot in configure.ac... -nfsv4, -nfsv41, etc...
>> I'm just following along with that.
> 
> I get that... but no-one has given a technical reason
> why disabling this code would even be necessary.
Nobody has see the code yet... :-)

There is a lot of churn in these patch.

> 
> 
>> Yes, at this point, nobody is asking to turn it off but
>> in future somebody may want to... due some security hole
>> or just make the footprint of the package smaller.
> 
> I'll bite. What is the added footprint of this patch
> series? I didn't think there was a new library dependency
> or anything like that...
Well mountd is now using an database and there
is a static reexport lib that a number daemons
and command like with...

In the I would like to bring (or be able) bring the
foot print of nfs-utils down so it will be more container
friendly... IDK if is possible... but that is the idea.

> 
> 
>> I've always though it was a good idea to be able
>> to turn things off.. esp if the feature will
>> not be used.
> 
> If there is a hazard to leaving it on all the time, we
> should find out now before the series is applied. So, is
> there harm to leaving it on all the time? That should be
> documented or fixed before merging.
Putting my distro maintainer hat on... If the flux
capacitor breaks and the server is no longer able
to exports things correctly... As I said there is
a lot of churn.... I would like a way to put things
back, so while we fix the flux capacitor, I can still
maintain a stable server.

I have found.... Have a way to get back...
is very useful! ;-)

steved.

> 
> I must be missing something.
> 
> 
>> steved.
>>
>>>> +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 */
>>>>
>>> --
>>> Chuck Lever
> 
> --
> Chuck Lever
> 
> 
>