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tdb: Reimplementation of Metze's "lib/tdb: if we know pwrite and pread are thread/fork safe tdb_reopen_all() should be a noop".

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This version just wraps the reopen code, so we still re-grab the lock and do
the normal sanity checks.

The reason we do this at all is to avoid global fd limits, see:
http://forums.fedoraforum.org/showthread.php?t=210393

Note also that this whole reopen concept is fundamentally racy: if the parent
goes away before the child calls tdb_reopen_all, the database can be left
without an active lock and another TDB_CLEAR_IF_FIRST opener will clear it.
A fork_with_tdbs() wrapper could use a pipe to solve this, but it's hardly
elegant (what if there are other independent things which have similar needs?).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
This commit is contained in:
Rusty Russell 2009-07-30 11:52:08 +09:30 committed by Stefan Metzmacher
parent fa91bc6719
commit 3b2f074bda
1 changed files with 10 additions and 5 deletions
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15
lib/tdb/common/open.c
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@ -425,6 +425,9 @@ int tdb_reopen(struct tdb_context *tdb)
goto fail;
}
/* If we have real pread & pwrite, we can skip reopen. */
#if !defined(LIBREPLACE_PREAD_NOT_REPLACED) || \
!defined(LIBREPLACE_PWRITE_NOT_REPLACED)
if (tdb_munmap(tdb) != 0) {
TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: munmap failed (%s)\n", strerror(errno)));
goto fail;
@ -436,11 +439,6 @@ int tdb_reopen(struct tdb_context *tdb)
TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: open failed (%s)\n", strerror(errno)));
goto fail;
}
if ((tdb->flags & TDB_CLEAR_IF_FIRST) &&
(tdb->methods->tdb_brlock(tdb, ACTIVE_LOCK, F_RDLCK, F_SETLKW, 0, 1) == -1)) {
TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: failed to obtain active lock\n"));
goto fail;
}
if (fstat(tdb->fd, &st) != 0) {
TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: fstat failed (%s)\n", strerror(errno)));
goto fail;
@ -450,6 +448,13 @@ int tdb_reopen(struct tdb_context *tdb)
goto fail;
}
tdb_mmap(tdb);
#endif /* fake pread or pwrite */
if ((tdb->flags & TDB_CLEAR_IF_FIRST) &&
(tdb->methods->tdb_brlock(tdb, ACTIVE_LOCK, F_RDLCK, F_SETLKW, 0, 1) == -1)) {
TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: failed to obtain active lock\n"));
goto fail;
}
return 0;