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Support read access on read-only media

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This commit is contained in:
Howard Chu 2012-10-13 04:05:00 -07:00
parent f037dd2d19
commit e40713b631
1 changed files with 52 additions and 25 deletions
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77
libraries/libmdb/mdb.c
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@ -913,6 +913,8 @@ struct MDB_env {
HANDLE me_mfd; /**< just for writing the meta pages */
/** Failed to update the meta page. Probably an I/O error. */
#define MDB_FATAL_ERROR 0x80000000U
/** Read-only Filesystem. Allow read access, no locking. */
#define MDB_ROFS 0x40000000U
uint32_t me_flags; /**< @ref mdb_env */
unsigned int me_psize; /**< size of a page, from #GET_PAGESIZE */
unsigned int me_maxreaders; /**< size of the reader table */
@ -1638,33 +1640,39 @@ mdb_txn_renew0(MDB_txn *txn)
txn->mt_dbxs = env->me_dbxs; /* mostly static anyway */
if (txn->mt_flags & MDB_TXN_RDONLY) {
MDB_reader *r = pthread_getspecific(env->me_txkey);
if (!r) {
pid_t pid = env->me_pid;
pthread_t tid = pthread_self();
if (env->me_flags & MDB_ROFS) {
i = mdb_env_pick_meta(env);
txn->mt_txnid = env->me_metas[i]->mm_txnid;
txn->mt_u.reader = NULL;
} else {
MDB_reader *r = pthread_getspecific(env->me_txkey);
if (!r) {
pid_t pid = env->me_pid;
pthread_t tid = pthread_self();
LOCK_MUTEX_R(env);
for (i=0; i<env->me_txns->mti_numreaders; i++)
if (env->me_txns->mti_readers[i].mr_pid == 0)
break;
if (i == env->me_maxreaders) {
LOCK_MUTEX_R(env);
for (i=0; i<env->me_txns->mti_numreaders; i++)
if (env->me_txns->mti_readers[i].mr_pid == 0)
break;
if (i == env->me_maxreaders) {
UNLOCK_MUTEX_R(env);
return MDB_READERS_FULL;
}
env->me_txns->mti_readers[i].mr_pid = pid;
env->me_txns->mti_readers[i].mr_tid = tid;
if (i >= env->me_txns->mti_numreaders)
env->me_txns->mti_numreaders = i+1;
/* Save numreaders for un-mutexed mdb_env_close() */
env->me_numreaders = env->me_txns->mti_numreaders;
UNLOCK_MUTEX_R(env);
return MDB_READERS_FULL;
r = &env->me_txns->mti_readers[i];
pthread_setspecific(env->me_txkey, r);
}
env->me_txns->mti_readers[i].mr_pid = pid;
env->me_txns->mti_readers[i].mr_tid = tid;
if (i >= env->me_txns->mti_numreaders)
env->me_txns->mti_numreaders = i+1;
/* Save numreaders for un-mutexed mdb_env_close() */
env->me_numreaders = env->me_txns->mti_numreaders;
UNLOCK_MUTEX_R(env);
r = &env->me_txns->mti_readers[i];
pthread_setspecific(env->me_txkey, r);
txn->mt_txnid = r->mr_txnid = env->me_txns->mti_txnid;
txn->mt_u.reader = r;
}
txn->mt_txnid = r->mr_txnid = env->me_txns->mti_txnid;
txn->mt_toggle = txn->mt_txnid & 1;
txn->mt_next_pgno = env->me_metas[txn->mt_toggle]->mm_last_pg+1;
txn->mt_u.reader = r;
} else {
LOCK_MUTEX_W(env);
@ -1804,7 +1812,8 @@ mdb_txn_reset0(MDB_txn *txn)
MDB_env *env = txn->mt_env;
if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) {
txn->mt_u.reader->mr_txnid = (txnid_t)-1;
if (!(env->me_flags & MDB_ROFS))
txn->mt_u.reader->mr_txnid = (txnid_t)-1;
} else {
MDB_oldpages *mop;
MDB_page *dp;
@ -2580,7 +2589,7 @@ mdb_env_open2(MDB_env *env, unsigned int flags)
MDB_meta meta;
MDB_page *p;
env->me_flags = flags;
env->me_flags |= flags;
memset(&meta, 0, sizeof(meta));
@ -2921,6 +2930,11 @@ mdb_env_setup_locks(MDB_env *env, char *lpath, int mode, int *excl)
if ((env->me_lfd = CreateFile(lpath, GENERIC_READ|GENERIC_WRITE,
FILE_SHARE_READ|FILE_SHARE_WRITE, NULL, OPEN_ALWAYS,
FILE_ATTRIBUTE_NORMAL, NULL)) == INVALID_HANDLE_VALUE) {
rc = ErrCode();
if (rc == ERROR_WRITE_PROTECT) {
env->me_flags |= MDB_ROFS;
return MDB_SUCCESS;
}
goto fail_errno;
}
/* Try to get exclusive lock. If we succeed, then
@ -2933,15 +2947,27 @@ mdb_env_setup_locks(MDB_env *env, char *lpath, int mode, int *excl)
#if !(O_CLOEXEC)
{
int fdflags;
if ((env->me_lfd = open(lpath, O_RDWR|O_CREAT, mode)) == -1)
if ((env->me_lfd = open(lpath, O_RDWR|O_CREAT, mode)) == -1) {
rc = ErrCode();
if (rc == EROFS) {
env->me_flags |= MDB_ROFS;
return MDB_SUCCESS;
}
goto fail_errno;
}
/* Lose record locks when exec*() */
if ((fdflags = fcntl(env->me_lfd, F_GETFD) | FD_CLOEXEC) >= 0)
fcntl(env->me_lfd, F_SETFD, fdflags);
}
#else /* O_CLOEXEC on Linux: Open file and set FD_CLOEXEC atomically */
if ((env->me_lfd = open(lpath, O_RDWR|O_CREAT|O_CLOEXEC, mode)) == -1)
if ((env->me_lfd = open(lpath, O_RDWR|O_CREAT|O_CLOEXEC, mode)) == -1) {
rc = ErrCode();
if (rc == EROFS) {
env->me_flags |= MDB_ROFS;
return MDB_SUCCESS;
}
goto fail_errno;
}
#endif
/* Try to get exclusive lock. If we succeed, then
@ -3128,6 +3154,7 @@ mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode)
sprintf(dpath, "%s" DATANAME, path);
}
env->me_flags = 0;
rc = mdb_env_setup_locks(env, lpath, mode, &excl);
if (rc)
goto leave;