From 99c452ae3f4d8d287ab4e34f8ffd967799d5ce95 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Tue, 14 Jan 2014 13:59:24 -0600 Subject: [PATCH] wimlib/header.h: Improve comments --- include/wimlib/header.h | 84 ++++++++++++++++++++++------------------- 1 file changed, 46 insertions(+), 38 deletions(-) diff --git a/include/wimlib/header.h b/include/wimlib/header.h index 2841b827..34e910cb 100644 --- a/include/wimlib/header.h +++ b/include/wimlib/header.h @@ -8,16 +8,18 @@ /* Length of "Globally Unique ID" field in WIM header. */ #define WIM_GID_LEN 16 -/* Length of the WIM header on disk. */ +/* Length of the WIM header on disk. wimlib currently requires that the header + * be exactly this size. */ #define WIM_HEADER_DISK_SIZE 208 /* Default WIM version number. Streams are always compressed independently. */ #define WIM_VERSION_DEFAULT 0x10d00 /* Version number used for WIMs that allow multiple streams packed into one - * resource (WIM_RESHDR_FLAG_PACKED_STREAMS). New as of Windows 8 WIMGAPI; used - * for the Windows 8 web downloader, but yet not yet properly documented by - * Microsoft. This WIM format also allows a new compression format (LZMS). */ + * resource ("solid blocks", marked by WIM_RESHDR_FLAG_PACKED_STREAMS) and also + * a new compression format (LZMS). This version is new as of Windows 8 + * WIMGAPI. Although it is used by Windows 8 web downloader, it is not yet + * properly documented by Microsoft. */ #define WIM_VERSION_PACKED_STREAMS 0xe00 /* Note: there is another WIM version from Vista pre-releases, but it is not @@ -46,10 +48,10 @@ ((u64)'\0' << 48) | \ ((u64)'\0' << 54)) -/* On-disk format of the WIM header. */ +/* On-disk format of the WIM header. */ struct wim_header_disk { - /* +0x00: Magic characters "MSWIM\0\0\0". */ + /* +0x00: Magic characters WIM_MAGIC or PWM_MAGIC. */ le64 magic; /* +0x08: Size of the WIM header, in bytes; WIM_HEADER_DISK_SIZE @@ -64,22 +66,25 @@ struct wim_header_disk { u32 wim_flags; /* +0x14: Uncompressed chunk size for compressed resources in the WIM - * other than packed resources, or 0 if the WIM is uncompressed. */ + * other than packed resources, or 0 if the WIM is uncompressed. + * (However wimlib will currently accept any value here if the WIM is + * uncompressed.) */ u32 chunk_size; /* +0x18: Globally unique identifier for the WIM file. Basically a - * bunch of random bytes. */ + * bunch of random bytes. */ u8 guid[WIM_GID_LEN]; /* +0x28: Number of this WIM part in the split WIM file, indexed from 1, - * or 1 if the WIM is not split. */ + * or 1 if the WIM is not split. */ u16 part_number; /* +0x2a: Total number of parts of the split WIM file, or 1 if the WIM - * is not split. */ + * is not split. */ u16 total_parts; - /* +0x2c: Number of images in the WIM. */ + /* +0x2c: Number of images in the WIM. WIMGAPI requires that this be at + * least 1. wimlib allows 0. */ u32 image_count; /* +0x30: Location and size of the WIM's lookup table. */ @@ -129,57 +134,60 @@ struct wim_header { struct wim_reshdr integrity_table_reshdr; }; -/* Flags for the `flags' field of the struct wim_header: */ +/* WIM header flags ('wim_flags' field of 'struct wim_header_disk'): */ -/* Reserved for future use */ +/* Reserved flag. */ #define WIM_HDR_FLAG_RESERVED 0x00000001 -/* Files and metadata in the WIM are compressed. */ +/* The WIM may contain compressed resources --- specifically, resources with + * WIM_RESHDR_FLAG_COMPRESSED set in their headers. Exactly one of the more + * specific WIM_HDR_FLAG_COMPRESSION_* flags must be set to specify the + * compression format used. */ #define WIM_HDR_FLAG_COMPRESSION 0x00000002 -/* WIM is read-only, so modifications should not be allowed even if the WIM is - * writable at the filesystem level. */ +/* The WIM is read-only, so modifications should not be allowed even if the WIM + * is writable at the filesystem level. */ #define WIM_HDR_FLAG_READONLY 0x00000004 -/* Resource data specified by images in this WIM may be contained in a different - * WIM. Or in other words, this WIM is part of a split WIM. */ +/* The WIM is part of a split WIM. */ #define WIM_HDR_FLAG_SPANNED 0x00000008 -/* The WIM contains resources only; no filesystem metadata. wimlib ignores this - * flag, as it looks for resources in all the WIMs anyway. */ +/* All streams included in the WIM's lookup table are non-metadata (do not have + * WIM_RESHDR_FLAG_METADATA set). wimlib ignores this flag and clears it on new + * WIM files it writes. */ #define WIM_HDR_FLAG_RESOURCE_ONLY 0x00000010 -/* The WIM contains metadata only. wimlib ignores this flag. Note that all the - * metadata resources for a split WIM should be in the first part. */ +/* All streams included in the WIM's lookup table are metadata (have + * WIM_RESHDR_FLAG_METADATA set). wimlib ignores this flag and clears it on + * new WIM files it writes. */ #define WIM_HDR_FLAG_METADATA_ONLY 0x00000020 /* The WIM is currently being written or appended to. */ #define WIM_HDR_FLAG_WRITE_IN_PROGRESS 0x00000040 -/* Reparse point fixup flag. See docs for --rpfix and --norpfix in imagex, or - * WIMLIB_ADD_FLAG_{RPFIX,NORPFIX} in wimlib.h. Note that - * WIM_HDR_FLAG_RP_FIX is a header flag and just sets the default behavior for - * the WIM; it can still be overridder on a per-image basis. But there is no - * flag to set the default behavior for a specific image. */ +/* Reparse point fixup flag. See docs for the --rpfix and --norpfix options to + * 'wimlib-imagex capture', or the WIMLIB_ADD_FLAG_{RPFIX,NORPFIX} flags in + * wimlib.h. Note that WIM_HDR_FLAG_RP_FIX is a header flag and just sets the + * default behavior for the WIM; it can still be programatically overridden on a + * per-image basis. But there is no flag in the file format to set the default + * behavior for a specific image. */ #define WIM_HDR_FLAG_RP_FIX 0x00000080 -/* Unused, reserved flag for another compression type */ +/* Unused, reserved flag for another compression type. */ #define WIM_HDR_FLAG_COMPRESS_RESERVED 0x00010000 -/* Resources within the WIM are compressed using "XPRESS" compression, which is - * a LZ77-based compression algorithm. */ +/* Resources in the WIM with WIM_RESHDR_FLAG_COMPRESSED set in their headers are + * compressed with XPRESS compression. */ #define WIM_HDR_FLAG_COMPRESS_XPRESS 0x00020000 -/* Resources within the WIM are compressed using "LZX" compression. This is also - * a LZ77-based algorithm. */ +/* Resources in the WIM with WIM_RESHDR_FLAG_COMPRESSED set in their headers are + * compressed with LZX compression. */ #define WIM_HDR_FLAG_COMPRESS_LZX 0x00040000 -/* Starting in Windows 8, WIMGAPI can create WIMs using LZMS compression, and - * this flag is set on such WIMs. However, an additional undocumented flag - * needs to be provided to WIMCreateFile() to create such WIMs, and the version - * number in the header of the resulting WIMs is different (3584). None of this - * is actually documented, and wimlib does not yet support this compression - * format. */ +/* Resources in the WIM with WIM_RESHDR_FLAG_COMPRESSED set in their headers are + * compressed with LZMS compression. Note: this flag is only valid if the WIM + * version is WIM_VERSION_PACKED_STREAMS. Also, this flag is only supported in + * wimlib v1.6.0 and later and WIMGAPI Windows 8 and later. */ #define WIM_HDR_FLAG_COMPRESS_LZMS 0x00080000 #endif /* _WIMLIB_HEADER_H */ -- 2.43.0