diff options
Diffstat (limited to 'src/os_unix.c')
| -rw-r--r-- | src/os_unix.c | 51 |
1 files changed, 38 insertions, 13 deletions
diff --git a/src/os_unix.c b/src/os_unix.c index a760e2c14..d463e5917 100644 --- a/src/os_unix.c +++ b/src/os_unix.c @@ -212,6 +212,7 @@ struct unixFile { UnixUnusedFd *pUnused; /* Pre-allocated UnixUnusedFd */ const char *zPath; /* Name of the file */ unixShm *pShm; /* Shared memory segment information */ + int readOnlyShm; /* True to open shared-memory read-only */ int szChunk; /* Configured by FCNTL_CHUNK_SIZE */ #if SQLITE_ENABLE_LOCKING_STYLE int openFlags; /* The flags specified at open() */ @@ -3452,6 +3453,10 @@ static int unixFileControl(sqlite3_file *id, int op, void *pArg){ case SQLITE_FCNTL_SIZE_HINT: { return fcntlSizeHint((unixFile *)id, *(i64 *)pArg); } + case SQLITE_FCNTL_READONLY_SHM: { + ((unixFile*)id)->readOnlyShm = (pArg!=0); + return SQLITE_OK; + } #ifndef NDEBUG /* The pager calls this method to signal that it has done ** a rollback and that the database is therefore unchanged and @@ -3541,6 +3546,7 @@ struct unixShmNode { char **apRegion; /* Array of mapped shared-memory regions */ int nRef; /* Number of unixShm objects pointing to this */ unixShm *pFirst; /* All unixShm objects pointing to this */ + u8 readOnly; /* True if this is a read-only mapping */ #ifdef SQLITE_DEBUG u8 exclMask; /* Mask of exclusive locks held */ u8 sharedMask; /* Mask of shared locks held */ @@ -3780,29 +3786,48 @@ static int unixOpenSharedMemory(unixFile *pDbFd){ } if( pInode->bProcessLock==0 ){ - pShmNode->h = robust_open(zShmFilename, O_RDWR|O_CREAT, - (sStat.st_mode & 0777)); + int flags = (pDbFd->readOnlyShm ? O_RDONLY : O_RDWR|O_CREAT); + pShmNode->h = robust_open(zShmFilename, flags, (sStat.st_mode & 0777)); if( pShmNode->h<0 ){ rc = unixLogError(SQLITE_CANTOPEN_BKPT, "open", zShmFilename); goto shm_open_err; } + pShmNode->readOnly = pDbFd->readOnlyShm; /* Check to see if another process is holding the dead-man switch. - ** If not, truncate the file to zero length. - */ - rc = SQLITE_OK; - if( unixShmSystemLock(pShmNode, F_WRLCK, UNIX_SHM_DMS, 1)==SQLITE_OK ){ - if( robust_ftruncate(pShmNode->h, 0) ){ - rc = unixLogError(SQLITE_IOERR_SHMOPEN, "ftruncate", zShmFilename); + ** If not, zero the first few bytes of the shared-memory file to make + ** sure it is not mistaken for valid by code in wal.c. Except, if this + ** is a read-only connection to the shared-memory then it is not possible + ** to check check if another process is holding a read-lock on the DMS + ** byte, as we cannot attempt a write-lock via a read-only file + ** descriptor. So in this case, we just assume the shared-memory + ** contents are Ok and proceed. */ + if( pShmNode->readOnly==0 ){ + rc = SQLITE_OK; + if( unixShmSystemLock(pShmNode, F_WRLCK, UNIX_SHM_DMS, 1)==SQLITE_OK ){ + if( pDbFd->readOnlyShm ){ + rc = SQLITE_IOERR_SHMOPEN; + }else if( 4!=osWrite(pShmNode->h, "\00\00\00\00", 4) ){ + rc = unixLogError(SQLITE_IOERR_SHMOPEN, "ftruncate", zShmFilename); + } } + if( rc==SQLITE_OK ){ + rc = unixShmSystemLock(pShmNode, F_RDLCK, UNIX_SHM_DMS, 1); + } + if( rc ) goto shm_open_err; } - if( rc==SQLITE_OK ){ - rc = unixShmSystemLock(pShmNode, F_RDLCK, UNIX_SHM_DMS, 1); - } - if( rc ) goto shm_open_err; } } + /* If the unixShmNode is read-only, but SQLITE_FCNTL_READONLY_SHM has not + ** been set for file-descriptor pDbFd, return an error. The wal.c module + ** will then call this function again with SQLITE_FCNTL_READONLY_SHM set. + */ + else if( pShmNode->readOnly && !pDbFd->readOnlyShm ){ + rc = SQLITE_IOERR_SHMOPEN; + goto shm_open_err; + } + /* Make the new connection a child of the unixShmNode */ p->pShmNode = pShmNode; #ifdef SQLITE_DEBUG @@ -3923,7 +3948,7 @@ static int unixShmMap( while(pShmNode->nRegion<=iRegion){ void *pMem; if( pShmNode->h>=0 ){ - pMem = mmap(0, szRegion, PROT_READ|PROT_WRITE, + pMem = mmap(0, szRegion, PROT_READ|(!pShmNode->readOnly?PROT_WRITE:0), MAP_SHARED, pShmNode->h, pShmNode->nRegion*szRegion ); if( pMem==MAP_FAILED ){ |