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Overview
Comment: | 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. |
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Downloads: | Tarball | ZIP archive |
Timelines: | family | ancestors | descendants | both | readonly-wal-recovery |
Files: | files | file ages | folders |
SHA3-256: |
5492f457dc7cc5c416de4b4e61e84bd2 |
User & Date: | dan 2017-10-26 17:05:22.656 |
Context
2017-10-26
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17:34 | Fix an error in the previous commit on this branch. (check-in: f71dfee06c user: dan tags: readonly-wal-recovery) | |
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) | |
Changes
Changes to src/os_unix.c.
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4141 4142 4143 4144 4145 4146 4147 | }; /* ** 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 */ | < | 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. */ |
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4163 4164 4165 4166 4167 4168 4169 4170 4171 4172 4173 4174 4175 4176 4177 4178 4179 4180 4181 4182 4183 | 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 | > > > > > > < | < < < < < < < | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 4162 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 | 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 ); /* 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 ); 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 { u16 mask; 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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4388 4389 4390 4391 4392 4393 4394 | /* 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); | | | | | > > > | > > > > > < < < < < < < | < < < < < < < < < | 4385 4386 4387 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 | /* 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); /* Check to see if another process is holding the dead-man switch. ** For a readonly_shm client, if no other process holds the DMS lock, ** the file cannot be opened and SQLITE_CANTOPEN_DIRTYWAL is returned. ** Or, for a read-write connection, if no other process holds a ** DMS lock the file is truncated to zero bytes in size. */ rc = SQLITE_OK; if( pShmNode->isReadonly ){ struct flock lock; lock.l_whence = SEEK_SET; lock.l_start = UNIX_SHM_DMS; lock.l_len = 1; lock.l_type = F_WRLCK; if( osFcntl(pShmNode->h, F_GETLK, &lockInfo)!=0 ) { rc = SQLITE_IOERR_LOCK; }else if( lock.l_type==F_UNLCK ){ rc = SQLITE_CANTOPEN_DIRTYWAL; } }else if( unixShmSystemLock(pDbFd, F_WRLCK, UNIX_SHM_DMS, 1)==SQLITE_OK ){ if( robust_ftruncate(pShmNode->h, 0) ){ rc = unixLogError(SQLITE_IOERR_SHMOPEN, "ftruncate", zShmFilename); } } if( rc==SQLITE_OK ){ rc = unixShmSystemLock(pDbFd, F_RDLCK, UNIX_SHM_DMS, 1); } if( rc ) goto shm_open_err; } } /* Make the new connection a child of the unixShmNode */ p->pShmNode = pShmNode; |
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