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Instead of extra locks, use F_GETLK to ensure that readonly_shm clients cannot

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connect to a wal-mode database if there are no writers.

FossilOrigin-Name: 5492f457dc7cc5c416de4b4e61e84bd2f10b4e6ce54011b7a60feb47f629c923
This commit is contained in:
dan 2017-10-26 17:05:22 +00:00
parent b5039fb7d3
commit 9181ae990a
3 changed files with 56 additions and 70 deletions
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17
manifest
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@ -1,5 +1,5 @@
C Use\sextra\slocks\sto\sprevent\sa\sreadonly_shm=1\sprocess\sfrom\sconnecting\sto\sa\nWAL-mode\sdatabase\sif\sthere\sare\sno\swriters.
D 2017-10-25T23:28:13.771
C Instead\sof\sextra\slocks,\suse\sF_GETLK\sto\sensure\sthat\sreadonly_shm\sclients\scannot\nconnect\sto\sa\swal-mode\sdatabase\sif\sthere\sare\sno\swriters.
D 2017-10-26T17:05:22.656
F Makefile.in e016061b23e60ac9ec27c65cb577292b6bde0307ca55abd874ab3487b3b1beb2
F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
F Makefile.msc 37740aba9c4bb359c627eadccf1cfd7be4f5f847078723777ea7763969e533b1
@ -447,7 +447,7 @@ F src/os.c 22d31db3ca5a96a408fbf1ceeaaebcaf64c87024d2ff9fe1cf2ddbec3e75c104
F src/os.h 48388821692e87da174ea198bf96b1b2d9d83be5dfc908f673ee21fafbe0d432
F src/os_common.h b2f4707a603e36811d9b1a13278bffd757857b85
F src/os_setup.h 0dbaea40a7d36bf311613d31342e0b99e2536586
F src/os_unix.c bec568f6f89e57b987f5ca38ae90087687d8e18669cd37eceb48ca6b56a8fbfb
F src/os_unix.c 8103f60342c65d501b4e58b381796648d6584b4814ffee79cd3a6e0c12fb6545
F src/os_win.c 6892c3ff23b7886577e47f13d827ca220c0831bae3ce00eea8c258352692f8c6
F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
F src/pager.c 07cf850241667874fcce9d7d924c814305e499b26c804322e2261247b5921903
@ -1666,10 +1666,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
P d4f893e1ae53a0445939ea2920af87d21dd36270494381028b2eaebe5c188f18
R 7c17d54c5cff309a6f13f49dd620b485
T *branch * readonly-wal-recovery
T *sym-readonly-wal-recovery *
T -sym-trunk *
U drh
Z 26f9af4fe6668c97b92039b43092c035
P 35d979082b4ab36d6a8975f8f15a50e69f46b72a173164d2b353377b9f758bd8
R 87551e9df4f45e3704d812374bd0d192
U dan
Z a113fb74c5589c985f30184211e03e42

2
manifest.uuid
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@ -1 +1 @@
35d979082b4ab36d6a8975f8f15a50e69f46b72a173164d2b353377b9f758bd8
5492f457dc7cc5c416de4b4e61e84bd2f10b4e6ce54011b7a60feb47f629c923

53
src/os_unix.c
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@ -4145,7 +4145,6 @@ struct unixShm {
*/
#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.
@ -4167,6 +4166,12 @@ static int unixShmSystemLock(
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));
@ -4181,15 +4186,7 @@ static int unixShmSystemLock(
/* 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 );
{ u16 mask;
OSTRACE(("SHM-LOCK "));
mask = ofst>31 ? 0xffff : (1<<(ofst+n)) - (1<<ofst);
if( rc==SQLITE_OK ){
@ -4392,38 +4389,30 @@ static int unixOpenSharedMemory(unixFile *pDbFd){
*/
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.
*/
/* 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 ){
if( !unixShmSystemLock(pDbFd, F_RDLCK, UNIX_SHM_DMS, UNIX_SHM_N_DMS) ){
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;
}
}
/* 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 ){
}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);
}
}
/* 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;
}