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Overview
Comment: | Use extra locks to prevent a readonly_shm=1 process from connecting to a WAL-mode database if there are no writers. |
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Downloads: | Tarball | ZIP archive |
Timelines: | family | ancestors | descendants | both | readonly-wal-recovery |
Files: | files | file ages | folders |
SHA3-256: |
35d979082b4ab36d6a8975f8f15a50e6 |
User & Date: | drh 2017-10-25 23:28:13.771 |
Context
2017-10-26
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17:05 | Instead of extra locks, use F_GETLK to ensure that readonly_shm clients cannot connect to a wal-mode database if there are no writers. (check-in: 5492f457dc user: dan tags: readonly-wal-recovery) | |
2017-10-25
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23:28 | Use extra locks to prevent a readonly_shm=1 process from connecting to a WAL-mode database if there are no writers. (check-in: 35d979082b user: drh tags: readonly-wal-recovery) | |
19:18 | Fix the sqlite3_dbpage virtual table so that it can read and write from any attached database. (check-in: d4f893e1ae user: drh tags: trunk) | |
Changes
Changes to src/os_unix.c.
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4141 4142 4143 4144 4145 4146 4147 4148 4149 4150 4151 4152 4153 4154 | }; /* ** Constants used for locking */ #define UNIX_SHM_BASE ((22+SQLITE_SHM_NLOCK)*4) /* first lock byte */ #define UNIX_SHM_DMS (UNIX_SHM_BASE+SQLITE_SHM_NLOCK) /* deadman switch */ /* ** Apply posix advisory locks for all bytes from ofst through ofst+n-1. ** ** Locks block if the mask is exactly UNIX_SHM_C and are non-blocking ** otherwise. */ | > | 4141 4142 4143 4144 4145 4146 4147 4148 4149 4150 4151 4152 4153 4154 4155 | }; /* ** Constants used for locking */ #define UNIX_SHM_BASE ((22+SQLITE_SHM_NLOCK)*4) /* first lock byte */ #define UNIX_SHM_DMS (UNIX_SHM_BASE+SQLITE_SHM_NLOCK) /* deadman switch */ #define UNIX_SHM_N_DMS 1000000000 /* Size of the DMS */ /* ** Apply posix advisory locks for all bytes from ofst through ofst+n-1. ** ** Locks block if the mask is exactly UNIX_SHM_C and are non-blocking ** otherwise. */ |
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4162 4163 4164 4165 4166 4167 4168 | struct flock f; /* The posix advisory locking structure */ int rc = SQLITE_OK; /* Result code form fcntl() */ /* Access to the unixShmNode object is serialized by the caller */ pShmNode = pFile->pInode->pShmNode; assert( sqlite3_mutex_held(pShmNode->mutex) || pShmNode->nRef==0 ); | < < < < < < > | > > > > > > > | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 4163 4164 4165 4166 4167 4168 4169 4170 4171 4172 4173 4174 4175 4176 4177 4178 4179 4180 4181 4182 4183 4184 4185 4186 4187 4188 4189 4190 4191 4192 4193 4194 4195 4196 4197 4198 4199 4200 4201 4202 4203 4204 4205 4206 4207 4208 4209 4210 4211 4212 4213 4214 4215 4216 4217 4218 4219 4220 4221 4222 4223 4224 4225 4226 4227 4228 | struct flock f; /* The posix advisory locking structure */ int rc = SQLITE_OK; /* Result code form fcntl() */ /* Access to the unixShmNode object is serialized by the caller */ pShmNode = pFile->pInode->pShmNode; assert( sqlite3_mutex_held(pShmNode->mutex) || pShmNode->nRef==0 ); if( pShmNode->h>=0 ){ /* Initialize the locking parameters */ memset(&f, 0, sizeof(f)); f.l_type = lockType; f.l_whence = SEEK_SET; f.l_start = ofst; f.l_len = n; rc = osFcntl(pShmNode->h, F_SETLK, &f); rc = (rc!=(-1)) ? SQLITE_OK : SQLITE_BUSY; } /* Update the global lock state and do debug tracing */ #ifdef SQLITE_DEBUG if( ofst<UNIX_SHM_DMS ){ u16 mask; /* Shared locks never span more than one byte */ assert( n==1 || lockType!=F_RDLCK ); /* Locks are within range */ assert( n>=1 && n<=SQLITE_SHM_NLOCK ); OSTRACE(("SHM-LOCK ")); mask = ofst>31 ? 0xffff : (1<<(ofst+n)) - (1<<ofst); if( rc==SQLITE_OK ){ if( lockType==F_UNLCK ){ OSTRACE(("unlock %d ok", ofst)); pShmNode->exclMask &= ~mask; pShmNode->sharedMask &= ~mask; }else if( lockType==F_RDLCK ){ OSTRACE(("read-lock %d ok", ofst)); pShmNode->exclMask &= ~mask; pShmNode->sharedMask |= mask; }else{ assert( lockType==F_WRLCK ); OSTRACE(("write-lock %d ok", ofst)); pShmNode->exclMask |= mask; pShmNode->sharedMask &= ~mask; } }else{ if( lockType==F_UNLCK ){ OSTRACE(("unlock %d failed", ofst)); }else if( lockType==F_RDLCK ){ OSTRACE(("read-lock failed")); }else{ assert( lockType==F_WRLCK ); OSTRACE(("write-lock %d failed", ofst)); } } OSTRACE((" - afterwards %03x,%03x\n", pShmNode->sharedMask, pShmNode->exclMask)); } #endif return rc; } /* |
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4385 4386 4387 4388 4389 4390 4391 | /* 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, ** the original owner will not be able to connect. */ robustFchown(pShmNode->h, sStat.st_uid, sStat.st_gid); | > | | > > > > > > > > > > > > > > > > > > > > | 4388 4389 4390 4391 4392 4393 4394 4395 4396 4397 4398 4399 4400 4401 4402 4403 4404 4405 4406 4407 4408 4409 4410 4411 4412 4413 4414 4415 4416 4417 4418 4419 4420 4421 4422 4423 4424 4425 4426 4427 4428 4429 4430 4431 4432 4433 | /* 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, ** the original owner will not be able to connect. */ robustFchown(pShmNode->h, sStat.st_uid, sStat.st_gid); /* Do not allow a read-only process to connect if there are no ** writers, because a read-only process is unable to recover the ** shm file following a system crash. */ rc = SQLITE_OK; if( pShmNode->isReadonly ){ if( !unixShmSystemLock(pDbFd, F_RDLCK, UNIX_SHM_DMS, UNIX_SHM_N_DMS) ){ rc = SQLITE_CANTOPEN_DIRTYWAL; } } /* If we are able to grab the dead-man switch, that means this is the ** first (write-enable) process to connect to the database. In that ** case, truncate the shm file because the contents found on disk might ** be invalid leftovers from a system crash. The shm will be rebuilt */ if( unixShmSystemLock(pDbFd, F_WRLCK, UNIX_SHM_DMS, 1)==SQLITE_OK ){ if( robust_ftruncate(pShmNode->h, 0) ){ rc = unixLogError(SQLITE_IOERR_SHMOPEN, "ftruncate", zShmFilename); } } /* Acquires locks to tell other processes that a this process is ** running and therefore the shm is valid they do not need to run ** recovery. */ if( rc==SQLITE_OK ){ unsigned r; rc = unixShmSystemLock(pDbFd, F_RDLCK, UNIX_SHM_DMS, 1); sqlite3_randomness(sizeof(r), &r); r = 1 + (r%(UNIX_SHM_N_DMS-1)); (void)unixShmSystemLock(pDbFd, F_WRLCK, UNIX_SHM_DMS+r, 1); } if( rc ) goto shm_open_err; } } /* Make the new connection a child of the unixShmNode */ p->pShmNode = pShmNode; |
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Changes to src/sqlite.h.in.
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504 505 506 507 508 509 510 511 512 513 514 515 516 517 | #define SQLITE_LOCKED_SHAREDCACHE (SQLITE_LOCKED | (1<<8)) #define SQLITE_BUSY_RECOVERY (SQLITE_BUSY | (1<<8)) #define SQLITE_BUSY_SNAPSHOT (SQLITE_BUSY | (2<<8)) #define SQLITE_CANTOPEN_NOTEMPDIR (SQLITE_CANTOPEN | (1<<8)) #define SQLITE_CANTOPEN_ISDIR (SQLITE_CANTOPEN | (2<<8)) #define SQLITE_CANTOPEN_FULLPATH (SQLITE_CANTOPEN | (3<<8)) #define SQLITE_CANTOPEN_CONVPATH (SQLITE_CANTOPEN | (4<<8)) #define SQLITE_CORRUPT_VTAB (SQLITE_CORRUPT | (1<<8)) #define SQLITE_READONLY_RECOVERY (SQLITE_READONLY | (1<<8)) #define SQLITE_READONLY_CANTLOCK (SQLITE_READONLY | (2<<8)) #define SQLITE_READONLY_ROLLBACK (SQLITE_READONLY | (3<<8)) #define SQLITE_READONLY_DBMOVED (SQLITE_READONLY | (4<<8)) #define SQLITE_ABORT_ROLLBACK (SQLITE_ABORT | (2<<8)) #define SQLITE_CONSTRAINT_CHECK (SQLITE_CONSTRAINT | (1<<8)) | > | 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 | #define SQLITE_LOCKED_SHAREDCACHE (SQLITE_LOCKED | (1<<8)) #define SQLITE_BUSY_RECOVERY (SQLITE_BUSY | (1<<8)) #define SQLITE_BUSY_SNAPSHOT (SQLITE_BUSY | (2<<8)) #define SQLITE_CANTOPEN_NOTEMPDIR (SQLITE_CANTOPEN | (1<<8)) #define SQLITE_CANTOPEN_ISDIR (SQLITE_CANTOPEN | (2<<8)) #define SQLITE_CANTOPEN_FULLPATH (SQLITE_CANTOPEN | (3<<8)) #define SQLITE_CANTOPEN_CONVPATH (SQLITE_CANTOPEN | (4<<8)) #define SQLITE_CANTOPEN_DIRTYWAL (SQLITE_CANTOPEN | (5<<8)) #define SQLITE_CORRUPT_VTAB (SQLITE_CORRUPT | (1<<8)) #define SQLITE_READONLY_RECOVERY (SQLITE_READONLY | (1<<8)) #define SQLITE_READONLY_CANTLOCK (SQLITE_READONLY | (2<<8)) #define SQLITE_READONLY_ROLLBACK (SQLITE_READONLY | (3<<8)) #define SQLITE_READONLY_DBMOVED (SQLITE_READONLY | (4<<8)) #define SQLITE_ABORT_ROLLBACK (SQLITE_ABORT | (2<<8)) #define SQLITE_CONSTRAINT_CHECK (SQLITE_CONSTRAINT | (1<<8)) |
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