}
/*
+ * finish_write():
+ *
* Finish writing a WIM file: write the lookup table, xml data, and integrity
- * table, then overwrite the WIM header. Always closes the WIM file descriptor
- * (wim->out_fd).
+ * table, then overwrite the WIM header. By default, closes the WIM file
+ * descriptor (@wim->out_fd) in both success and error cases.
*
* write_flags is a bitwise OR of the following:
*
* (public) WIMLIB_WRITE_FLAG_FSYNC:
* fsync() the output file before closing it.
*
- * (public) WIMLIB_WRITE_FLAG_PIPABLE:
+ * (public) WIMLIB_WRITE_FLAG_PIPABLE:
* Writing a pipable WIM, possibly to a pipe; include pipable WIM
* stream headers before the lookup table and XML data, and also
* write the WIM header at the end instead of seeking to the
* Instead of overwriting the WIM header at the beginning of the
* file, simply append it to the end of the file. (Used when
* writing to pipe.)
+ * (private) WIMLIB_WRITE_FLAG_FILE_DESCRIPTOR:
+ * Do not close the file descriptor @wim->out_fd on either success
+ * on failure.
* (private) WIMLIB_WRITE_FLAG_USE_EXISTING_TOTALBYTES:
* Use the existing <TOTALBYTES> stored in the in-memory XML
* information, rather than setting it to the offset of the XML
if (ret)
goto out_close_wim;
+ /* Write integrity table (optional). */
if (write_flags & WIMLIB_WRITE_FLAG_CHECK_INTEGRITY) {
if (write_flags & WIMLIB_WRITE_FLAG_CHECKPOINT_AFTER_XML) {
struct wim_header checkpoint_hdr;
if (ret)
goto out_close_wim;
} else {
+ /* No integrity table. */
zero_resource_entry(&wim->hdr.integrity);
}
+ /* Now that all information in the WIM header has been determined, the
+ * preliminary header written earlier can be overwritten, the header of
+ * the existing WIM file can be overwritten, or the final header can be
+ * written to the end of the pipable WIM. */
wim->hdr.flags &= ~WIM_HDR_FLAG_WRITE_IN_PROGRESS;
hdr_offset = 0;
if (write_flags & WIMLIB_WRITE_FLAG_HEADER_AT_END)
if (ret)
goto out_close_wim;
+ /* Possibly sync file data to disk before closing. On POSIX systems, it
+ * is necessary to do this before using rename() to overwrite an
+ * existing file with a new file. Otherwise, data loss would occur if
+ * the system is abruptly terminated when the metadata for the rename
+ * operation has been written to disk, but the new file data has not.
+ */
if (write_flags & WIMLIB_WRITE_FLAG_FSYNC) {
if (fsync(wim->out_fd.fd)) {
ERROR_WITH_ERRNO("Error syncing data to WIM file");
#endif
/*
+ * write_pipable_wim():
+ *
* Perform the intermediate stages of creating a "pipable" WIM (i.e. a WIM
- * capable of being applied from a pipe). Such a WIM looks like:
+ * capable of being applied from a pipe).
*
* Pipable WIMs are a wimlib-specific modification of the WIM format such that
* images can be applied from them sequentially when the file data is sent over
*
* - Magic characters in header are "WLPWM\0\0\0" (wimlib pipable WIM) instead
* of "MSWIM\0\0\0". This lets wimlib know that the WIM is pipable and also
- * should stop other software from trying to read the file as a normal WIM.
+ * stops other software from trying to read the file as a normal WIM.
*
* - The header at the beginning of the file does not contain all the normal
* information; in particular it will have all 0's for the lookup table and
* uncompressed stream size, and flags that indicate whether the stream is
* compressed. The data of uncompressed streams then follows literally, while
* the data of compressed streams follows in a modified format. Compressed
- * streams have no chunk table, since the chunk table cannot be written until
- * all chunks have been compressed; instead, each compressed chunk is prefixed
- * by a `struct pwm_chunk_hdr' that gives its size. However, the offsets are
- * given in the chunk table as if these chunk headers were not present.
+ * streams do not begin with a chunk table, since the chunk table cannot be
+ * written until all chunks have been compressed. Instead, each compressed
+ * chunk is prefixed by a `struct pwm_chunk_hdr' that gives its size.
+ * Furthermore, the chunk table is written at the end of the resource instead
+ * of the start. Note: chunk offsets are given in the chunk table as if the
+ * `struct pwm_chunk_hdr's were not present; also, the chunk table is only
+ * used if the WIM is being read from a seekable file (not a pipe).
*
* - Metadata resources always come before other file resources (streams).
* (This does not by itself constitute an incompatibility with normal WIMs,
*
* Layout of pipable WIM:
*
- * ----------+----------+--------------------+----------------+--------------+------------+--------+
- * | Header | XML data | Metadata resources | File resources | Lookup table | XML data | Header |
- * ----------+----------+--------------------+----------------+--------------+------------+--------+
+ * ---------+----------+--------------------+----------------+--------------+-----------+--------+
+ * | Header | XML data | Metadata resources | File resources | Lookup table | XML data | Header |
+ * ---------+----------+--------------------+----------------+--------------+-----------+--------+
*
* Layout of normal WIM:
*
- * +---------+--------------------+----------------+--------------+----------+
- * | Header | Metadata resources | File resources | Lookup table | XML data |
- * +---------+--------------------+----------------+--------------+----------+
+ * +--------+-----------------------------+-------------------------+
+ * | Header | File and metadata resources | Lookup table | XML data |
+ * +--------+-----------------------------+-------------------------+
+ *
+ * An optional integrity table can follow the final XML data in both normal and
+ * pipable WIMs. However, due to implementation details, wimlib currently can
+ * only include an integrity table in a pipable WIM when writing it to a
+ * seekable file (not a pipe).
*
* Do note that since pipable WIMs are not supported by Microsoft's software,
* wimlib does not create them unless explicitly requested (with