[git commit] tar: store negative mtime as 0; pack very large files using base-256 encoding

Denys Vlasenko vda.linux at googlemail.com
Wed May 4 19:14:12 UTC 2011


commit: http://git.busybox.net/busybox/commit/?id=9180c6045e8b2465b3e18a22eb08ee8438ae8544
branch: http://git.busybox.net/busybox/commit/?id=refs/heads/master

function                                             old     new   delta
writeTarHeader                                       841     979    +138

Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 archival/tar.c    |   36 ++++++++++++++++++++++++++++++++----
 include/archive.h |    2 +-
 2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/archival/tar.c b/archival/tar.c
index 01b83d5..ebaa183 100644
--- a/archival/tar.c
+++ b/archival/tar.c
@@ -264,7 +264,8 @@ static int writeTarHeader(struct TarBallInfo *tbInfo,
 	PUT_OCTAL(header.uid, statbuf->st_uid);
 	PUT_OCTAL(header.gid, statbuf->st_gid);
 	memset(header.size, '0', sizeof(header.size)-1); /* Regular file size is handled later */
-	PUT_OCTAL(header.mtime, statbuf->st_mtime);
+	/* users report that files with negative st_mtime cause trouble, so: */
+	PUT_OCTAL(header.mtime, statbuf->st_mtime >= 0 ? statbuf->st_mtime : 0);
 
 	/* Enter the user and group names */
 	safe_strncpy(header.uname, get_cached_username(statbuf->st_uid), sizeof(header.uname));
@@ -316,15 +317,42 @@ static int writeTarHeader(struct TarBallInfo *tbInfo,
 	} else if (S_ISFIFO(statbuf->st_mode)) {
 		header.typeflag = FIFOTYPE;
 	} else if (S_ISREG(statbuf->st_mode)) {
-		if (sizeof(statbuf->st_size) > 4
-		 && statbuf->st_size > (off_t)0777777777777LL
+		/* header.size field is 12 bytes long */
+		/* Does octal-encoded size fit? */
+		uoff_t filesize = statbuf->st_size;
+		if (sizeof(filesize) <= 4
+		 || filesize <= (uoff_t)0777777777777LL
 		) {
+			PUT_OCTAL(header.size, filesize);
+		}
+		/* Does base256-encoded size fit?
+		 * It always does unless off_t is wider than 64 bits.
+		 */
+		else if (ENABLE_FEATURE_TAR_GNU_EXTENSIONS
+#if ULLONG_MAX > 0xffffffffffffffffLL /* 2^64-1 */
+		 && (filesize <= 0x3fffffffffffffffffffffffLL)
+#endif
+		) {
+	                /* GNU tar uses "base-256 encoding" for very large numbers.
+	                 * Encoding is binary, with highest bit always set as a marker
+	                 * and sign in next-highest bit:
+	                 * 80 00 .. 00 - zero
+	                 * bf ff .. ff - largest positive number
+	                 * ff ff .. ff - minus 1
+	                 * c0 00 .. 00 - smallest negative number
+			 */
+			char *p8 = header.size + sizeof(header.size);
+			do {
+				*--p8 = (uint8_t)filesize;
+				filesize >>= 8;
+			} while (p8 != header.size);
+			*p8 |= 0x80;
+		} else {
 			bb_error_msg_and_die("can't store file '%s' "
 				"of size %"OFF_FMT"u, aborting",
 				fileName, statbuf->st_size);
 		}
 		header.typeflag = REGTYPE;
-		PUT_OCTAL(header.size, statbuf->st_size);
 	} else {
 		bb_error_msg("%s: unknown file type", fileName);
 		return FALSE;
diff --git a/include/archive.h b/include/archive.h
index b139dc5..9e176d3 100644
--- a/include/archive.h
+++ b/include/archive.h
@@ -125,7 +125,7 @@ typedef struct archive_handle_t {
 #define TAR_BLOCK_SIZE 512
 #define NAME_SIZE      100
 #define NAME_SIZE_STR "100"
-typedef struct tar_header_t {       /* byte offset */
+typedef struct tar_header_t {     /* byte offset */
 	char name[NAME_SIZE];     /*   0-99 */
 	char mode[8];             /* 100-107 */
 	char uid[8];              /* 108-115 */
-- 
1.7.3.4



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