From b0a6bbcba9dc23f4722827cb13fb0efff5e2799d Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Wed, 22 May 2013 15:57:50 -0500 Subject: [PATCH] dentry.c, dentry.h: Comment dentry structures better --- include/wimlib/dentry.h | 81 ++++++++++++++++------------- src/dentry.c | 112 ++++++++++++++++++++++++++++++++++++++-- 2 files changed, 154 insertions(+), 39 deletions(-) diff --git a/include/wimlib/dentry.h b/include/wimlib/dentry.h index dfb5a95b..05fcd2f3 100644 --- a/include/wimlib/dentry.h +++ b/include/wimlib/dentry.h @@ -126,7 +126,9 @@ ads_entries_have_same_name(const struct wim_ads_entry *entry_1, * dentry_tree_fix_inodes() in hardlink.c). */ struct wim_dentry { - /* The inode for this dentry */ + /* Pointer to the inode for this dentry. This will contain some + * information that was factored out of the on-disk WIM dentry as common + * to all dentries in a hard link group. */ struct wim_inode *d_inode; /* Node for the parent's red-black tree of child dentries, sorted by @@ -155,70 +157,79 @@ struct wim_dentry { * including the terminating null character. */ u32 full_path_nbytes; - /* Does this dentry need to be extracted? */ + /* For extraction operations, a subtree of dentries will have this flag + * set so we can keep track of which dentries still need to be + * extracted. Otherwise this will always be 0. */ u8 needs_extraction : 1; + /* For extraction operations, this flag will be set when a dentry in the + * tree being extracted is not being extracted for some reason (file + * type not supported by target filesystem or contains invalid + * characters). Otherwise this will always be 0. */ u8 not_extracted : 1; - /* Only used during NTFS capture */ + /* When capturing from a NTFS volume using NTFS-3g, this flag is set on + * dentries that were created from a filename in the WIN32 or WIN32+DOS + * namespaces rather than the POSIX namespace. Otherwise this will + * always be 0. */ u8 is_win32_name : 1; - /* Set to 1 if an inode has multiple DOS names. */ + /* When verifying the dentry tree after reading it into memory, this + * flag will be set on all dentries in a hard link group that have a + * nonempty DOS name except one. This is because it is supposed to be + * illegal (on NTFS, at least) for a single inode to have multiple DOS + * names. */ u8 dos_name_invalid : 1; - /* Temporary list */ + /* Temporary list field used to make lists of dentries in a few places. + * */ struct list_head tmp_list; - /* List of dentries in the inode (hard link set) */ + /* Linked list node that places this dentry in the list of aliases for + * its inode (d_inode) */ struct list_head d_alias; /* The parent of this directory entry. */ struct wim_dentry *parent; - /* - * Size of directory entry on disk, in bytes. Typical size is around - * 104 to 120 bytes. - * - * It is possible for the length field to be 0. This situation, which - * is undocumented, indicates the end of a list of sibling nodes in a - * directory. It also means the real length is 8, because the dentry - * included only the length field, but that takes up 8 bytes. - * - * The length here includes the base directory entry on disk as well as - * the long and short filenames. It does NOT include any alternate - * stream entries that may follow the directory entry, even though the - * size of those needs to be considered. The length SHOULD be 8-byte - * aligned, although we don't require it to be. We do require the - * length to be large enough to hold the file name(s) of the dentry; - * additionally, a warning is issued if this field is larger than the - * aligned size. - */ + /* 'length' and 'subdir_offset' are only used while reading and writing + * this dentry; see the corresponding field in + * `struct wim_dentry_on_disk' for explanation. */ u64 length; - - /* The offset, from the start of the uncompressed WIM metadata resource - * for this image, of this dentry's child dentries. 0 if the directory - * entry has no children, which is the case for regular files or reparse - * points. */ u64 subdir_offset; + /* These correspond to the two unused fields in the on-disk WIM dentry; + * we read them into memory so we can write them unchanged. These + * fields are set to 0 on new dentries. */ u64 d_unused_1; u64 d_unused_2; - /* Pointer to the UTF-16LE short filename (malloc()ed buffer) */ + /* Pointer to the UTF-16LE short filename (malloc()ed buffer), or NULL + * if this dentry has no short name. */ utf16lechar *short_name; - /* Pointer to the UTF-16LE filename (malloc()ed buffer). */ + /* Pointer to the UTF-16LE filename (malloc()ed buffer), or NULL if this + * dentry has no filename. */ utf16lechar *file_name; - /* Full path of this dentry in the WIM */ + /* Full path to this dentry in the WIM, in platform-dependent "tchars" + * that can be printed without convension. By default this field will + * be NULL and will only be calculated on-demand by the + * calculate_dentry_full_path() or dentry_full_path() functions. */ tchar *_full_path; - /* Actual name to extract this dentry as. */ + /* (Extraction only) Actual name to extract this dentry as, along with + * its length in tchars excluding the NULL terminator. This usually + * will be the same as file_name, with the character encoding converted + * if needed. But if file_name contains characters not accepted on the + * current platform, then this may be set slightly differently from + * file_name. This will be either NULL or a malloc()ed buffer that may + * alias file_name. */ tchar *extraction_name; size_t extraction_name_nchars; - /* List head for building a list of dentries that contain a certain - * stream. */ + /* (Extraction only) List head for building a list of dentries that + * contain a certain stream. */ struct list_head extraction_stream_list; }; diff --git a/src/dentry.c b/src/dentry.c index b948859c..435a7c91 100644 --- a/src/dentry.c +++ b/src/dentry.c @@ -72,18 +72,108 @@ struct wim_ads_entry_on_disk { #define WIM_ADS_ENTRY_DISK_SIZE 38 -/* WIM directory entry (on-disk format) */ +/* On-disk format of a WIM dentry (directory entry), located in the metadata + * resource for a WIM image. */ struct wim_dentry_on_disk { + + /* Length of this directory entry in bytes, not including any alternate + * data stream entries. Should be a multiple of 8 so that the following + * dentry or alternate data stream entry is aligned on an 8-byte + * boundary. (If not, wimlib will round it up.) + * + * It is also possible for this field to be 0. This situation, which is + * undocumented, indicates the end of a list of sibling nodes in a + * directory. It also means the real length is 8, because the dentry + * included only the length field, but that takes up 8 bytes. */ le64 length; + + /* Attributes of the file or directory. This is a bitwise OR of the + * FILE_ATTRIBUTE_* constants and should correspond to the value + * retrieved by GetFileAttributes() on Windows. */ le32 attributes; + + /* A value that specifies the security descriptor for this file or + * directory. If -1, the file or directory has no security descriptor. + * Otherwise, it is a 0-based index into the WIM image's table of + * security descriptors (see: `struct wim_security_data') */ sle32 security_id; + + /* Offset from the start of the uncompressed metadata resource of this + * directory's child directory entries, or 0 if this directory entry + * does not correspond to a directory or otherwise does not have any + * children. */ le64 subdir_offset; + + /* Reserved fields */ le64 unused_1; le64 unused_2; + + /* The following three time fields should correspond to those gotten by + * calling GetFileTime() on Windows. */ + + /* Creation time, in 100-nanosecond intervals since January 1, 1601. */ le64 creation_time; + + /* Last access time, in 100-nanosecond intervals since January 1, 1601. */ le64 last_access_time; + + /* Last write time, in 100-nanosecond intervals since January 1, 1601. */ le64 last_write_time; + + /* Vaguely, the SHA-1 message digest ("hash") of the file's contents. + * More specifically, this is for the "unnamed data stream" rather than + * any "alternate data streams". This hash value is used to look up the + * corresponding entry in the WIM's stream lookup table to actually find + * the file contents within the WIM. + * + * If the file has no unnamed data stream (e.g. is a directory), then + * this field will be all zeroes. If the unnamed data stream is empty + * (i.e. an "empty file"), then this field is also expected to be all + * zeroes. (It will be if wimlib created the WIM image, at least; + * otherwise it can't be ruled out that the SHA-1 message digest of 0 + * bytes of data is given explicitly.) + * + * If the file has reparse data, then this field will instead specify + * the SHA-1 message digest of the reparse data. If it is somehow + * possible for a file to have both an unnamed data stream and reparse + * data, then this is not handled by wimlib. + * + * As a further special case, if this field is all zeroes but there is + * an alternate data stream entry with no name and a nonzero SHA-1 + * message digest field, then that hash must be used instead of this + * one. (wimlib does not use this quirk on WIM images it creates.) + */ u8 unnamed_stream_hash[SHA1_HASH_SIZE]; + + /* The format of the following data is not yet completely known and they + * do not correspond to Microsoft's documentation. + * + * If this directory entry is for a reparse point (has + * FILE_ATTRIBUTE_REPARSE_POINT set in the attributes field), then the + * version of the following fields containing the reparse tag is valid. + * Furthermore, the field notated as not_rpfixed, as far as I can tell, + * is supposed to be set to 1 if reparse point fixups (a.k.a. fixing the + * targets of absolute symbolic links) were done, and otherwise 0. + * + * If this directory entry is not for a reparse point, then the version + * of the following fields containing the hard_link_group_id is valid. + * All MS says about this field is that "If this file is part of a hard + * link set, all the directory entries in the set will share the same + * value in this field.". However, more specifically I have observed + * the following: + * - If the file is part of a hard link set of size 1, then the + * hard_link_group_id should be set to either 0, which is treated + * specially as indicating "not hardlinked", or any unique value. + * - The specific nonzero values used to identity hard link sets do + * not matter, as long as they are unique. + * - However, due to bugs in Microsoft's software, it is actually NOT + * guaranteed that directory entries that share the same hard link + * group ID are actually hard linked to each either. We have to + * handle this by using special code to use distinguishing features + * (possible because some information about the underlying inode is + * repeated in each dentry) to split up these fake hard link groups + * into what they actually are supposed to be. + */ union { struct { le32 rp_unknown_1; @@ -96,14 +186,28 @@ struct wim_dentry_on_disk { le64 hard_link_group_id; } _packed_attribute nonreparse; }; + + /* Number of alternate data stream entries that directly follow this + * dentry on-disk. */ le16 num_alternate_data_streams; + + /* Length of this file's UTF-16LE encoded short name (8.3 DOS-compatible + * name), if present, in bytes, excluding the null terminator. If this + * file has no short name, then this field should be 0. */ le16 short_name_nbytes; + + /* Length of this file's UTF-16LE encoded "long" name, excluding the + * null terminator. If this file has no short name, then this field + * should be 0. It's expected that only the root dentry has this field + * set to 0. */ le16 file_name_nbytes; - /* Follewed by variable length file name, if file_name_nbytes != 0 */ + /* Follewed by variable length file name, in UTF16-LE, if + * file_name_nbytes != 0. Includes null terminator. */ utf16lechar file_name[]; - /* Followed by variable length short name, if short_name_nbytes != 0 */ + /* Followed by variable length short name, in UTF16-LE, if + * short_name_nbytes != 0. Includes null terminator. */ /*utf16lechar short_name[];*/ } _packed_attribute; @@ -1723,7 +1827,7 @@ read_dentry(const u8 * restrict metadata_resource, u64 metadata_resource_len, * fixed-length fields */ if (dentry->length < sizeof(struct wim_dentry_on_disk)) { ERROR("Directory entry has invalid length of %"PRIu64" bytes", - dentry->length); + entry->length); return WIMLIB_ERR_INVALID_DENTRY; } -- 2.43.0