When opening the *-shm file for a readonly database, try to open it in read-write mode before falling back to readonly. This is in case some other read/write connection within the same process uses the same file descriptor.

FossilOrigin-Name: a07c581e88aa4d9835f6144c0fd5e58ef42f14ac

manifest

@@ -1,5 +1,5 @@
-C Merge\supdates\sfor\sversion\s3.15.1.
-D 2016-11-04T19:09:39.851
+C When\sopening\sthe\s*-shm\sfile\sfor\sa\sreadonly\sdatabase,\stry\sto\sopen\sit\sin\sread-write\smode\sbefore\sfalling\sback\sto\sreadonly.\sThis\sis\sin\scase\ssome\sother\sread/write\sconnection\swithin\sthe\ssame\sprocess\suses\sthe\ssame\sfile\sdescriptor.
+D 2016-11-17T14:02:50.490
 F Makefile.in c9c70541089a9755069a9dad0b609cf14a382649
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc a8af814f63c124db048517b63a0b8650c3fc26fc
@@ -374,7 +374,7 @@ F src/os.c c03b50496df5815e8f6d45bae4404b73cadf069b
 F src/os.h 8e976e59eb4ca1c0fca6d35ee803e38951cb0343
 F src/os_common.h b2f4707a603e36811d9b1a13278bffd757857b85
 F src/os_setup.h 0dbaea40a7d36bf311613d31342e0b99e2536586
-F src/os_unix.c 5f558f9433256f25d2f2dd852c7e93a84c05e1e4
+F src/os_unix.c ab6fb76945f600f7e557ca6d7c59dc23e327be70
 F src/os_win.c 4224bff1904dfdf3664680897e1b5077de1fd649
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c 3fea5fb3694c36870dc18730f914a52ed838b507
@@ -1402,7 +1402,7 @@ F test/walnoshm.test 559b878f3aab838971d820329ca35f1caa7b038e
 F test/waloverwrite.test dad2f26567f1b45174e54fbf9a8dc1cb876a7f03
 F test/walpersist.test abd956d66e2f36d2d9d05d3a969f48be6d2ddbec
 F test/walprotocol.test 0b92feb132ccebd855494d917d3f6c2d717ace20
-F test/walro.test 310f5f364e64eaaa2f2233229a7b602ccb038bc9
+F test/walro.test 2baad492f8f52d24143ec8a0a811dc5604d05ae9
 F test/walshared.test 04590b10c677f75318701818c50bc0dda5da64ab
 F test/walslow.test 07a51cbe9d4895d0a90c7af76d14a62d363ac162
 F test/walthread.test c13f5a12fbd9d81e58f49875dc9dd8a52a84cf03
@@ -1535,7 +1535,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 06014163475051b7f3b3570e8af434362bbc5b87 b86b79c442a58d10aa005ba4f34095375a88d242
-R bcb3efeba01d0af0aee999d16c1330b7
-U drh
-Z 6f3c15f758e9fbdf4e4bd5482bd7aa1f
+P 0e5ffd9123d6d2d2b8f3701e8a73cc98a3a7ff5f
+R dd715a7090f8ccbb07a44c145e36e97f
+U dan
+Z dc2784f452c216a6da4c2c53fde33522

manifest.uuid

@@ -1 +1 @@
-0e5ffd9123d6d2d2b8f3701e8a73cc98a3a7ff5f
+a07c581e88aa4d9835f6144c0fd5e58ef42f14ac

src/os_unix.c

@@ -5048,20 +5048,33 @@ static int unixOpenSharedMemory(unixFile *pDbFd){
 
     if( pInode->bProcessLock==0 ){
       int openFlags = O_RDWR | O_CREAT;
-      if( sqlite3_uri_boolean(pDbFd->zPath, "readonly_shm", 0)
-#if defined(SQLITE_ENABLE_PERSIST_WAL)&&(SQLITE_ENABLE_LOCKING_STYLE \
-    || defined(__APPLE__))
-         || (pDbFd->openFlags & O_RDWR) != O_RDWR
-#endif
-         ){
+      int fd;                     /* File descriptor for *-shm file */
+      if( sqlite3_uri_boolean(pDbFd->zPath, "readonly_shm", 0) ){
         openFlags = O_RDONLY;
         pShmNode->isReadonly = 1;
       }
-      pShmNode->h = robust_open(zShmFilename, openFlags, (sStat.st_mode&0777));
-      if( pShmNode->h<0 ){
+      fd = robust_open(zShmFilename, openFlags, (sStat.st_mode&0777));
+
+      /* If it was not possible to open the *-shm file in read/write mode,
+      ** and the database file itself has been opened in read-only mode,
+      ** try to open the *-shm file in read-only mode as well. Even if the
+      ** database connection is read-only, it is still better to try opening
+      ** the *-shm file in read/write mode first, as the same file descriptor
+      ** may be also be used by a read/write database connection.  */
+#if defined(SQLITE_ENABLE_PERSIST_WAL)&&(SQLITE_ENABLE_LOCKING_STYLE \
+    || defined(__APPLE__))
+      if( fd<0 && errno!=EISDIR && pShmNode->isReadonly==0 
+       && (pDbFd->openFlags & O_RDWR)!=O_RDWR
+      ){
+        fd = robust_open(zShmFilename, O_RDONLY, (sStat.st_mode&0777));
+        pShmNode->isReadonly = 1;
+      }
+#endif
+      if( fd<0 ){
         rc = unixLogError(SQLITE_CANTOPEN_BKPT, "open", zShmFilename);
         goto shm_open_err;
       }
+      pShmNode->h = fd;
 
       /* If this process is running as root, make sure that the SHM file
       ** is owned by the same user that owns the original database.  Otherwise,

test/walro.test

@@ -306,4 +306,62 @@ do_multiclient_test tn {
 
 forcedelete $shmpath
 
+#----------------------------------------------------------------------------
+
+catch {db2 close}
+reset_db
+do_execsql_test 3.1 {
+  CREATE TABLE t1(a, b);
+  PRAGMA journal_mode = wal;
+  INSERT INTO t1 VALUES(1, 2);
+} {wal}
+db_save
+db close
+db_restore
+
+sqlite3 db test.db -readonly 1
+
+do_execsql_test 3.2 { SELECT * FROM t1 } {1 2}
+do_catchsql_test 3.3 { 
+  INSERT INTO t1 VALUES(3, 4) 
+} {1 {attempt to write a readonly database}}
+
+sqlite3 db2 test.db
+do_test 3.4 { 
+  db2 eval { INSERT INTO t1 VALUES(3, 4) }
+} {}
+do_execsql_test 3.5 { SELECT * FROM t1 } {1 2 3 4}
+
+db close
+db2 close
+db_restore
+file attributes $shmpath -permissions r--r--r--
+sqlite3 db test.db -readonly 1
+do_execsql_test 3.6 { SELECT * FROM t1 } {1 2}
+
+db close
+db_restore
+file attributes $shmpath -permissions r--r--r--
+sqlite3 db test.db
+do_test 3.7 {
+  catchsql { SELECT * FROM t1 } 
+} {1 {unable to open database file}}
+
+db close
+db_restore
+file attributes $shmpath -permissions r--r--r--
+sqlite3 db test.db -readonly 1
+do_execsql_test 3.8 { SELECT * FROM t1 } {1 2}
+
+sqlite3 db2 test.db
+do_test 3.9 { db2 eval { SELECT * FROM t1 } } {1 2}
+do_test 3.10 { 
+  catchsql { INSERT INTO t1 VALUES(3, 4) } db2 
+} {1 {attempt to write a readonly database}}
+
+catch { db close }
+catch { db2 close }
+
+forcedelete $shmpath
+
 finish_test