Use mkdir() and rmdir() rather than open() and unlink() to create the lock

files with the unix-dotlock VFS.  The change is backwards compatible and,
we are told, works better on some network filesystems.

FossilOrigin-Name: e2f08426d7a84a2ac6148f485b7af377201a175b

manifest

@@ -1,5 +1,5 @@
-C Enhance\sthe\sshell\sso\sthat\sthe\s".schema"\scommand\sworks\swith\scase\sinsensitive\nLIKE\spatterns\seven\swith\sPRAGMA\scache_sensitive_like=ON.
-D 2011-11-04T00:35:56.173
+C Use\smkdir()\sand\srmdir()\srather\sthan\sopen()\sand\sunlink()\sto\screate\sthe\slock\nfiles\swith\sthe\sunix-dotlock\sVFS.\s\sThe\schange\sis\sbackwards\scompatible\sand,\nwe\sare\stold,\sworks\sbetter\son\ssome\snetwork\sfilesystems.
+D 2011-11-04T02:24:02.845
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in a162fe39e249b8ed4a65ee947c30152786cfe897
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -166,7 +166,7 @@ F src/os.c 5d9b02782ed36345348d6fe21d7762ed3a9cfd2a
 F src/os.h 9dbed8c2b9c1f2f2ebabc09e49829d4777c26bf9
 F src/os_common.h 92815ed65f805560b66166e3583470ff94478f04
 F src/os_os2.c 4a75888ba3dfc820ad5e8177025972d74d7f2440
-F src/os_unix.c ddda0b1c5ae536669634d7bff31b3f8f4d654866
+F src/os_unix.c 32f2ac2adbbba6acb649915a6953524ecf4cf9d5
 F src/os_win.c 49d418916428a59d773f39993db0ecde56ab4c37
 F src/pager.c ad62daa0c21e27ae332b3ceb4f579a2a97046ddc
 F src/pager.h 9f81b08efb06db4ba8be69446e10b005c351373d
@@ -699,7 +699,7 @@ F test/subselect.test d24fd8757daf97dafd2e889c73ea4c4272dcf4e4
 F test/substr.test 18f57c4ca8a598805c4d64e304c418734d843c1a
 F test/superlock.test 7b1167925e9d30a5d1f0701d24812fdda42c3a86
 F test/sync.test a34cd43e98b7fb84eabbf38f7ed8f7349b3f3d85
-F test/syscall.test 966addf703faee6a5d509abe6d8885e393e552fd
+F test/syscall.test 2a922050dbee032f587249b070fb42692f5e1e22
 F test/sysfault.test c79441d88d23696fbec7b147dba98d42a04f523f
 F test/table.test a59d985ca366e39b17b175f387f9d5db5a18d4e2
 F test/tableapi.test 2674633fa95d80da917571ebdd759a14d9819126
@@ -974,7 +974,7 @@ F tool/tostr.awk e75472c2f98dd76e06b8c9c1367f4ab07e122d06
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
 F tool/warnings-clang.sh 9f406d66e750e8ac031c63a9ef3248aaa347ef2a
 F tool/warnings.sh fbc018d67fd7395f440c28f33ef0f94420226381
-P 6f9898db7ff0730cc03f561f9c32ef3dee7e5d81
-R d2ce493b65686d96618972d4df6ad36c
+P b06bf3b3605a3c39cdfbb76c9a9f6b5202bb95ec
+R 044a4088718b0a84e4c3090a9efafe25
 U drh
-Z 773ddc7cfde2cddd1397075b47c1fbba
+Z 61f6de61b36ef0e121c72533e9e5fa9c

manifest.uuid

@@ -1 +1 @@
-b06bf3b3605a3c39cdfbb76c9a9f6b5202bb95ec
+e2f08426d7a84a2ac6148f485b7af377201a175b

src/os_unix.c

@@ -407,6 +407,12 @@ static struct unix_syscall {
   { "openDirectory",    (sqlite3_syscall_ptr)openDirectory,      0 },
 #define osOpenDirectory ((int(*)(const char*,int*))aSyscall[17].pCurrent)
 
+  { "mkdir",        (sqlite3_syscall_ptr)mkdir,           0 },
+#define osMkdir     ((int(*)(const char*,mode_t))aSyscall[18].pCurrent)
+
+  { "rmdir",        (sqlite3_syscall_ptr)rmdir,           0 },
+#define osRmdir     ((int(*)(const char*))aSyscall[19].pCurrent)
+
 }; /* End of the overrideable system calls */
 
 /*
@@ -1845,8 +1851,8 @@ static int nolockClose(sqlite3_file *id) {
 ************************* Begin dot-file Locking ******************************
 **
 ** The dotfile locking implementation uses the existance of separate lock
-** files in order to control access to the database.  This works on just
-** about every filesystem imaginable.  But there are serious downsides:
+** files (really a directory) to control access to the database.  This works
+** on just about every filesystem imaginable.  But there are serious downsides:
 **
 **    (1)  There is zero concurrency.  A single reader blocks all other
 **         connections from reading or writing the database.
@@ -1857,15 +1863,15 @@ static int nolockClose(sqlite3_file *id) {
 ** Nevertheless, a dotlock is an appropriate locking mode for use if no
 ** other locking strategy is available.
 **
-** Dotfile locking works by creating a file in the same directory as the
-** database and with the same name but with a ".lock" extension added.
-** The existance of a lock file implies an EXCLUSIVE lock.  All other lock
-** types (SHARED, RESERVED, PENDING) are mapped into EXCLUSIVE.
+** Dotfile locking works by creating a subdirectory in the same directory as
+** the database and with the same name but with a ".lock" extension added.
+** The existance of a lock directory implies an EXCLUSIVE lock.  All other
+** lock types (SHARED, RESERVED, PENDING) are mapped into EXCLUSIVE.
 */
 
 /*
 ** The file suffix added to the data base filename in order to create the
-** lock file.
+** lock directory.
 */
 #define DOTLOCK_SUFFIX ".lock"
 
@@ -1932,7 +1938,6 @@ static int dotlockCheckReservedLock(sqlite3_file *id, int *pResOut) {
 */
 static int dotlockLock(sqlite3_file *id, int eFileLock) {
   unixFile *pFile = (unixFile*)id;
-  int fd;
   char *zLockFile = (char *)pFile->lockingContext;
   int rc = SQLITE_OK;
 
@@ -1952,9 +1957,9 @@ static int dotlockLock(sqlite3_file *id, int eFileLock) {
   }
   
   /* grab an exclusive lock */
-  fd = robust_open(zLockFile,O_RDONLY|O_CREAT|O_EXCL,0600);
-  if( fd<0 ){
-    /* failed to open/create the file, someone else may have stolen the lock */
+  rc = osMkdir(zLockFile, 0777);
+  if( rc<0 ){
+    /* failed to open/create the lock directory */
     int tErrno = errno;
     if( EEXIST == tErrno ){
       rc = SQLITE_BUSY;
@@ -1966,7 +1971,6 @@ static int dotlockLock(sqlite3_file *id, int eFileLock) {
     }
     return rc;
   } 
-  robust_close(pFile, fd, __LINE__);
   
   /* got it, set the type and return ok */
   pFile->eFileLock = eFileLock;
@@ -1985,6 +1989,7 @@ static int dotlockLock(sqlite3_file *id, int eFileLock) {
 static int dotlockUnlock(sqlite3_file *id, int eFileLock) {
   unixFile *pFile = (unixFile*)id;
   char *zLockFile = (char *)pFile->lockingContext;
+  int rc;
 
   assert( pFile );
   OSTRACE(("UNLOCK  %d %d was %d pid=%d (dotlock)\n", pFile->h, eFileLock,
@@ -2006,7 +2011,9 @@ static int dotlockUnlock(sqlite3_file *id, int eFileLock) {
   
   /* To fully unlock the database, delete the lock file */
   assert( eFileLock==NO_LOCK );
-  if( osUnlink(zLockFile) ){
+  rc = osRmdir(zLockFile);
+  if( rc<0 && errno==ENOTDIR ) rc = osUnlink(zLockFile);
+  if( rc<0 ){
     int rc = 0;
     int tErrno = errno;
     if( ENOENT != tErrno ){
@@ -5715,7 +5722,7 @@ static int proxyCreateLockPath(const char *lockPath){
       if( i-start>2 || (i-start==1 && buf[start] != '.' && buf[start] != '/') 
          || (i-start==2 && buf[start] != '.' && buf[start+1] != '.') ){
         buf[i]='\0';
-        if( mkdir(buf, SQLITE_DEFAULT_PROXYDIR_PERMISSIONS) ){
+        if( osMkdir(buf, SQLITE_DEFAULT_PROXYDIR_PERMISSIONS) ){
           int err=errno;
           if( err!=EEXIST ) {
             OSTRACE(("CREATELOCKPATH  FAILED creating %s, "
@@ -6751,7 +6758,7 @@ int sqlite3_os_init(void){
 
   /* Double-check that the aSyscall[] array has been constructed
   ** correctly.  See ticket [bb3a86e890c8e96ab] */
-  assert( ArraySize(aSyscall)==18 );
+  assert( ArraySize(aSyscall)==20 );
 
   /* Register all VFSes defined in the aVfs[] array */
   for(i=0; i<(sizeof(aVfs)/sizeof(sqlite3_vfs)); i++){

test/syscall.test

@@ -59,7 +59,7 @@ do_test 2.1.2 { test_syscall exists nosuchcall } 0
 foreach s {
     open close access getcwd stat fstat ftruncate
     fcntl read pread write pwrite fchmod fallocate
-    pread64 pwrite64 unlink openDirectory
+    pread64 pwrite64 unlink openDirectory mkdir rmdir
 } {
   if {[test_syscall exists $s]} {lappend syscall_list $s}
 }