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Overview
| Comment: | Fix the wal-index header read routine so that it correctly detects a zero header as being malformed and in need of a wal-index rebuild. |
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| Downloads: | Tarball | ZIP archive |
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA1: |
1a4eb3a3efe86c7caff4d9a5894953bc |
| User & Date: | drh 2010-05-21 13:16:19.000 |
Context
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2010-05-21
| ||
| 15:31 | Remove entries from wal-index hash tables when a rollback or savepoint rollback occurs. (check-in: 36795c2b23 user: dan tags: trunk) | |
| 13:16 | Fix the wal-index header read routine so that it correctly detects a zero header as being malformed and in need of a wal-index rebuild. (check-in: 1a4eb3a3ef user: drh tags: trunk) | |
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2010-05-20
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| 23:51 | Add a new xShmBarrier method to the VFS - a shared-memory fence operation. Implement the same in both unix and win32. Use it to make the WAL subsystem more robust. (check-in: 1bd011c9fe user: drh tags: trunk) | |
Changes
Changes to src/wal.c.
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** and *pChanged is set to 1.
**
** If the checksum cannot be verified return non-zero. If the header
** is read successfully and the checksum verified, return zero.
*/
int walIndexTryHdr(Wal *pWal, int *pChanged){
u32 aCksum[2]; /* Checksum on the header content */
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** and *pChanged is set to 1.
**
** If the checksum cannot be verified return non-zero. If the header
** is read successfully and the checksum verified, return zero.
*/
int walIndexTryHdr(Wal *pWal, int *pChanged){
u32 aCksum[2]; /* Checksum on the header content */
WalIndexHdr h1, h2; /* Two copies of the header content */
WalIndexHdr *aHdr; /* Header in shared memory */
assert( pWal->pWiData );
if( pWal->szWIndex==0 ){
/* The wal-index is of size 0 bytes. This is handled in the same way
** as an invalid header. The caller will run recovery to construct
** a valid wal-index file before accessing the database.
*/
return 1;
}
/* Read the header. The caller may or may not have an exclusive
** (WRITE, PENDING, CHECKPOINT or RECOVER) lock on the wal-index
** file, meaning it is possible that an inconsistent snapshot is read
** from the file. If this happens, return non-zero.
**
** There are two copies of the header at the beginning of the wal-index.
** When reading, read [0] first then [1]. Writes are in the reverse order.
** Memory barriers are used to prevent the compiler or the hardware from
** reordering the reads and writes.
*/
aHdr = (WalIndexHdr*)pWal->pWiData;
memcpy(&h1, &aHdr[0], sizeof(h1));
sqlite3OsShmBarrier(pWal->pDbFd);
memcpy(&h2, &aHdr[1], sizeof(h2));
if( memcmp(&h1, &h2, sizeof(h1))!=0 ){
return 1; /* Dirty read */
}
if( h1.szPage==0 ){
return 1; /* Malformed header - probably all zeros */
}
walChecksumBytes((u8*)&h1, sizeof(h1)-sizeof(h1.aCksum), 0, aCksum);
if( aCksum[0]!=h1.aCksum[0] || aCksum[1]!=h1.aCksum[1] ){
return 1; /* Checksum does not match */
}
if( memcmp(&pWal->hdr, &h1, sizeof(WalIndexHdr)) ){
*pChanged = 1;
memcpy(&pWal->hdr, &h1, sizeof(WalIndexHdr));
pWal->szPage = pWal->hdr.szPage;
}
/* The header was successfully read. Return zero. */
return 0;
}
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