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Optionally support shared-memory in /dev/shm or other tmpfs directory

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using an unsupported compile-time option.

FossilOrigin-Name: 534aab837e5a34fd58963ab2b505bfbb9da2e8ee
This commit is contained in:
drh
2010-07-15 18:32:40 +00:00
parent 1e5de5a13d
commit a4ced195db
3 changed files with 52 additions and 25 deletions
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51
src/os_unix.c
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@@ -3282,13 +3282,22 @@ static void unixShmPurge(unixFile *pFd){
** as the open database file and has the same name as the open database
** file with the "-shm" suffix added. For example, if the database file
** is "/home/user1/config.db" then the file that is created and mmapped
** for shared memory will be called "/home/user1/config.db-shm". We
** experimented with using files in /dev/tmp or an some other tmpfs mount.
** But if a file in a different directory from the database file is used,
** then differing access permissions or a chroot() might cause two different
** processes on the same database to end up using different files for
** shared memory - meaning that their memory would not really be shared -
** resulting in database corruption.
** for shared memory will be called "/home/user1/config.db-shm".
**
** Another approach to is to use files in /dev/shm or /dev/tmp or an
** some other tmpfs mount. But if a file in a different directory
** from the database file is used, then differing access permissions
** or a chroot() might cause two different processes on the same
** database to end up using different files for shared memory -
** meaning that their memory would not really be shared - resulting
** in database corruption. Nevertheless, this tmpfs file usage
** can be enabled at compile-time using -DSQLITE_SHM_DIRECTORY="/dev/shm"
** or the equivalent. The use of the SQLITE_SHM_DIRECTORY compile-time
** option results in an incompatible build of SQLite; builds of SQLite
** that with differing SQLITE_SHM_DIRECTORY settings attempt to use the
** same database file at the same time, database corruption will likely
** result. The SQLITE_SHM_DIRECTORY compile-time option is considered
** "unsupported" and may go away in a future SQLite release.
**
** When opening a new shared-memory file, if no other instances of that
** file are currently open, in this process or in other processes, then
@@ -3327,7 +3336,11 @@ static int unixOpenSharedMemory(unixFile *pDbFd){
goto shm_open_err;
}
#ifdef SQLITE_SHM_DIRECTORY
nShmFilename = sizeof(SQLITE_SHM_DIRECTORY) + 30;
#else
nShmFilename = 5 + (int)strlen(pDbFd->zPath);
#endif
pShmNode = sqlite3_malloc( sizeof(*pShmNode) + nShmFilename );
if( pShmNode==0 ){
rc = SQLITE_NOMEM;
@@ -3335,7 +3348,13 @@ static int unixOpenSharedMemory(unixFile *pDbFd){
}
memset(pShmNode, 0, sizeof(*pShmNode));
zShmFilename = pShmNode->zFilename = (char*)&pShmNode[1];
#ifdef SQLITE_SHM_DIRECTORY
sqlite3_snprintf(nShmFilename, zShmFilename,
SQLITE_SHM_DIRECTORY "/sqlite-shm-%x-%x",
(u32)sStat.st_ino, (u32)sStat.st_dev);
#else
sqlite3_snprintf(nShmFilename, zShmFilename, "%s-shm", pDbFd->zPath);
#endif
pShmNode->h = -1;
pDbFd->pInode->pShmNode = pShmNode;
pShmNode->pInode = pDbFd->pInode;
@@ -4311,14 +4330,13 @@ static UnixUnusedFd *findReusableFd(const char *zPath, int flags){
**
** If the file being opened is a temporary file, it is always created with
** the octal permissions 0600 (read/writable by owner only). If the file
** is a database or master journal file, it is created with the permissions
** mask SQLITE_DEFAULT_FILE_PERMISSIONS.
** is a database, journal or master journal file, it is created with the
** permissions mask SQLITE_DEFAULT_FILE_PERMISSIONS.
**
** Finally, if the file being opened is a WAL or regular journal file, then
** this function queries the file-system for the permissions on the
** corresponding database file and sets *pMode to this value. Whenever
** possible, WAL and journal files are created using the same permissions
** as the associated database file.
** Finally, if the file being opened is a WAL file, then this function
** queries the file-system for the permissions on the corresponding database
** file and sets *pMode to this value. Whenever possible, WAL files are
** created using the same permissions as the associated database file.
*/
static int findCreateFileMode(
const char *zPath, /* Path of file (possibly) being created */
@@ -4326,12 +4344,12 @@ static int findCreateFileMode(
mode_t *pMode /* OUT: Permissions to open file with */
){
int rc = SQLITE_OK; /* Return Code */
if( flags & (SQLITE_OPEN_WAL|SQLITE_OPEN_MAIN_JOURNAL) ){
if( flags & SQLITE_OPEN_WAL ){
char zDb[MAX_PATHNAME+1]; /* Database file path */
int nDb; /* Number of valid bytes in zDb */
struct stat sStat; /* Output of stat() on database file */
nDb = sqlite3Strlen30(zPath) - ((flags & SQLITE_OPEN_WAL) ? 4 : 8);
nDb = sqlite3Strlen30(zPath) - 4;
memcpy(zDb, zPath, nDb);
zDb[nDb] = '\0';
if( 0==stat(zDb, &sStat) ){
@@ -4474,7 +4492,6 @@ static int unixOpen(
rc = findCreateFileMode(zName, flags, &openMode);
if( rc!=SQLITE_OK ){
assert( !p->pUnused );
assert( eType==SQLITE_OPEN_WAL || eType==SQLITE_OPEN_MAIN_JOURNAL );
return rc;
}
fd = open(zName, openFlags, openMode);