os_fid.c
上传用户:romrleung
上传日期:2022-05-23
资源大小:18897k
文件大小:4k
- /*-
- * See the file LICENSE for redistribution information.
- *
- * Copyright (c) 1996-2002
- * Sleepycat Software. All rights reserved.
- */
- #include "db_config.h"
- #ifndef lint
- static const char revid[] = "$Id: os_fid.c,v 11.15 2002/08/26 14:37:39 margo Exp $";
- #endif /* not lint */
- #include "db_int.h"
- #define SERIAL_INIT 0
- static u_int32_t fid_serial = SERIAL_INIT;
- /*
- * __os_fileid --
- * Return a unique identifier for a file.
- */
- int
- __os_fileid(dbenv, fname, unique_okay, fidp)
- DB_ENV *dbenv;
- const char *fname;
- int unique_okay;
- u_int8_t *fidp;
- {
- size_t i;
- u_int32_t tmp;
- u_int8_t *p;
- int ret;
- /*
- * The documentation for GetFileInformationByHandle() states that the
- * inode-type numbers are not constant between processes. Actually,
- * they are, they're the NTFS MFT indexes. So, this works on NTFS,
- * but perhaps not on other platforms, and perhaps not over a network.
- * Can't think of a better solution right now.
- */
- DB_FH fh;
- BY_HANDLE_FILE_INFORMATION fi;
- BOOL retval = FALSE;
- DB_ASSERT(fname != NULL);
- /* Clear the buffer. */
- memset(fidp, 0, DB_FILE_ID_LEN);
- /*
- * Initialize/increment the serial number we use to help avoid
- * fileid collisions. Note that we don't bother with locking;
- * it's unpleasant to do from down in here, and if we race on
- * this no real harm will be done, since the finished fileid
- * has so many other components.
- *
- * We increment by 100000 on each call as a simple way of
- * randomizing; simply incrementing seems potentially less useful
- * if pids are also simply incremented, since this is process-local
- * and we may be one of a set of processes starting up. 100000
- * pushes us out of pid space on most platforms, and has few
- * interesting properties in base 2.
- */
- if (fid_serial == SERIAL_INIT)
- __os_id(&fid_serial);
- else
- fid_serial += 100000;
- /*
- * First we open the file, because we're not given a handle to it.
- * If we can't open it, we're in trouble.
- */
- if ((ret = __os_open(dbenv, fname, DB_OSO_RDONLY, _S_IREAD, &fh)) != 0)
- return (ret);
- /* File open, get its info */
- if ((retval = GetFileInformationByHandle(fh.handle, &fi)) == FALSE)
- ret = __os_win32_errno();
- __os_closehandle(dbenv, &fh);
- if (retval == FALSE)
- return (ret);
- /*
- * We want the three 32-bit words which tell us the volume ID and
- * the file ID. We make a crude attempt to copy the bytes over to
- * the callers buffer.
- *
- * We don't worry about byte sexing or the actual variable sizes.
- *
- * When this routine is called from the DB access methods, it's only
- * called once -- whatever ID is generated when a database is created
- * is stored in the database file's metadata, and that is what is
- * saved in the mpool region's information to uniquely identify the
- * file.
- *
- * When called from the mpool layer this routine will be called each
- * time a new thread of control wants to share the file, which makes
- * things tougher. As far as byte sexing goes, since the mpool region
- * lives on a single host, there's no issue of that -- the entire
- * region is byte sex dependent. As far as variable sizes go, we make
- * the simplifying assumption that 32-bit and 64-bit processes will
- * get the same 32-bit values if we truncate any returned 64-bit value
- * to a 32-bit value.
- */
- tmp = (u_int32_t)fi.nFileIndexLow;
- for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
- *fidp++ = *p++;
- tmp = (u_int32_t)fi.nFileIndexHigh;
- for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
- *fidp++ = *p++;
- if (unique_okay) {
- /*
- * Use the system time to try to get a unique value
- * within this process. A millisecond counter
- * overflows 32 bits in about 49 days. So we use 8
- * bytes, and don't bother with the volume ID, which
- * is not very useful for our purposes.
- */
- SYSTEMTIME st;
- GetSystemTime(&st);
- tmp = (st.wYear - 1900) * 12 + (st.wMonth - 1);
- for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
- *fidp++ = *p++;
- tmp = ((((st.wDay - 1) * 24 + st.wHour) * 60 +
- st.wMinute) * 60 + st.wSecond) * 1000 +
- st.wMilliseconds;
- for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
- *fidp++ = *p++;
- for (p = (u_int8_t *)&fid_serial, i = sizeof(u_int32_t);
- i > 0; --i)
- *fidp++ = *p++;
- } else {
- tmp = (u_int32_t)fi.dwVolumeSerialNumber;
- for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
- *fidp++ = *p++;
- }
- return (0);
- }