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Add experimental support for read-only connections to WAL databases.

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FossilOrigin-Name: bb59f9862da45d25fb51d7821130854828c91c98
This commit is contained in:
dan
2011-05-10 17:31:29 +00:00
parent de941c3756
commit 4edc6bf3ee
8 changed files with 227 additions and 43 deletions
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51
src/os_unix.c
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@@ -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 ){