Support read access on read-only media

diff --git a/libraries/libmdb/mdb.c b/libraries/libmdb/mdb.c
index 15432178c2150678ef28b9d66a6126684ba35d0e..9bfe2f8d1fc7814743e60c8b08ebb042a816cf05 100644 (file)
--- a/libraries/libmdb/mdb.c
+++ b/libraries/libmdb/mdb.c
@@ -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();
-
-                       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) {
+               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) {
+                                       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;