sqlite3源码理解-sqlite3_open

一、源码下载

从网站下载sqlite-src-3330000.zip.
https://www.sqlite.org/download.html

二、sqlite3_open

在linux系统下，当应用程序调用sqlite3_open时，最终会调用open函数创建或打开一个数据库文件，如下图所示:

三、xOpen

在sqlite3OsOpen()函数中，调用linux vfs的xOpen函数:

  rc = pVfs->xOpen(pVfs, zPath, pFile, flags & 0x1087f7f, pFlagsOut);
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pVfs在sqlite3_vfs_find()函数中会被指定为unix， pVfs-xOpen实际为unixOpen:

int sqlite3_os_init(void){ 
  #define UNIXVFS(VFSNAME, FINDER) {                        \
    3,                    /* iVersion */                    \
    sizeof(unixFile),     /* szOsFile */                    \
    MAX_PATHNAME,         /* mxPathname */                  \
    0,                    /* pNext */                       \
    VFSNAME,              /* zName */                       \
    (void*)&FINDER,       /* pAppData */                    \
    unixOpen,             /* xOpen */                       \
    unixDelete,           /* xDelete */                     \
    unixAccess,           /* xAccess */                     \
    unixFullPathname,     /* xFullPathname */               \
    unixDlOpen,           /* xDlOpen */                     \
    unixDlError,          /* xDlError */                    \
    unixDlSym,            /* xDlSym */                      \
    unixDlClose,          /* xDlClose */                    \
    unixRandomness,       /* xRandomness */                 \
    unixSleep,            /* xSleep */                      \
    unixCurrentTime,      /* xCurrentTime */                \
    unixGetLastError,     /* xGetLastError */               \
    unixCurrentTimeInt64, /* xCurrentTimeInt64 */           \
    unixSetSystemCall,    /* xSetSystemCall */              \
    unixGetSystemCall,    /* xGetSystemCall */              \
    unixNextSystemCall,   /* xNextSystemCall */             \
  }
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unixOpen()调用robust_open:

fd = robust_open(zName, openFlags, openMode);
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robust_open()调用osOpen():

if( osOpen("/dev/null", O_RDONLY, m)<0 ) break;
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osOpen()被定义为posixOpen():

//Os_unix.c
static struct unix_syscall {
  const char *zName;            /* Name of the system call */
  sqlite3_syscall_ptr pCurrent; /* Current value of the system call */
  sqlite3_syscall_ptr pDefault; /* Default value */
} aSyscall[] = {
  { "open",         (sqlite3_syscall_ptr)posixOpen,  0  },
#define osOpen      ((int(*)(const char*,int,int))aSyscall[0].pCurrent)

  { "close",        (sqlite3_syscall_ptr)close,      0  },
#define osClose     ((int(*)(int))aSyscall[1].pCurrent)
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posixOpen调用linux系统调用open:

static int posixOpen(const char *zFile, int flags, int mode){
  return open(zFile, flags, mode);
}
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