[PATCH] GIT: Create tar archives of tree on the fly

Write commit ID to global extended pax header at the beginning of the tar
file, if possible.  get-tar-commit-id.c is an example program to get the
ID back out of such a tar archive.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/get-tar-commit-id.c b/get-tar-commit-id.c
new file mode 100644 (file)
index 0000000..a1a17e5
--- /dev/null
+++ b/get-tar-commit-id.c
@@ -0,0 +1,27 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#define HEADERSIZE     1024
+
+int main(int argc, char **argv)
+{
+       char buffer[HEADERSIZE];
+       ssize_t n;
+
+       n = read(0, buffer, HEADERSIZE);
+       if (n < HEADERSIZE) {
+               fprintf(stderr, "read error\n");
+               return 3;
+       }
+       if (buffer[156] != 'g')
+               return 1;
+       if (memcmp(&buffer[512], "52 comment=", 11))
+               return 1;
+       n = write(1, &buffer[523], 41);
+       if (n < 41) {
+               fprintf(stderr, "write error\n");
+               return 2;
+       }
+       return 0;
+}

diff --git a/tar-tree.c b/tar-tree.c
index 5cc7cfe..ea7ea91 100644 (file)
--- a/tar-tree.c
+++ b/tar-tree.c
@@ -160,7 +160,7 @@ static unsigned int path_len(int is_dir, const char *basepath,
        return len;
 }
 
-static void write_header(const char *, const char *, struct path_prefix *,
+static void write_header(const char *, char, const char *, struct path_prefix *,
                          const char *, unsigned int, unsigned long);
 
 /* stores a pax extended header directly in the block buffer */
@@ -169,7 +169,7 @@ static void write_extended_header(const char *headerfilename, int is_dir,
                                   struct path_prefix *prefix,
                                   const char *path, unsigned int namelen)
 {
-       char *records, *p;
+       char *p;
        unsigned int size = 1 + 6 + namelen + 1;
        if (size > 9)
                size++;
@@ -177,12 +177,10 @@ static void write_extended_header(const char *headerfilename, int is_dir,
                size++;
        if (size > RECORDSIZE)
                die("tar-tree: extended header too big, wtf?");
-       write_header(NULL, NULL, NULL, headerfilename, 0100600, size);
-
-       records = block + offset;
-       memset(records, 0, RECORDSIZE);
+       write_header(NULL, 'x', NULL, NULL, headerfilename, 0100600, size);
+       p = block + offset;
+       memset(p, 0, RECORDSIZE);
        offset += RECORDSIZE;
-       p = records;
        append_long(&p, size);
        append_string(&p, " path=");
        append_path(&p, is_dir, basepath, prefix, path);
@@ -190,8 +188,22 @@ static void write_extended_header(const char *headerfilename, int is_dir,
        write_if_needed();
 }
 
+static void write_global_extended_header(const char *sha1)
+{
+       char *p;
+       write_header(NULL, 'g', NULL, NULL, "pax_global_header", 0, 52);
+       p = block + offset;
+       memset(p, 0, RECORDSIZE);
+       offset += RECORDSIZE;
+       append_long(&p, 52);    /* 2 + 9 + 40 + 1 */
+       append_string(&p, " comment=");
+       append_string(&p, sha1_to_hex(sha1));
+       append_char(&p, '\n');
+       write_if_needed();
+}
+
 /* stores a ustar header directly in the block buffer */
-static void write_header(const char *sha1, const char *basepath,
+static void write_header(const char *sha1, char typeflag, const char *basepath,
                          struct path_prefix *prefix, const char *path,
                          unsigned int mode, unsigned long size)
 {
@@ -236,11 +248,7 @@ static void write_header(const char *sha1, const char *basepath,
        sprintf(&header[124], "%011lo", S_ISDIR(mode) ? 0 : size);
        sprintf(&header[136], "%011lo", archive_time);
 
-       /* typeflag */
-       if (!sha1)
-               header[156] = 'x';      /* extended header */
-       else
-               header[156] = S_ISDIR(mode) ? '5' : '0';
+       header[156] = typeflag;
 
        memcpy(&header[257], "ustar", 6);
        memcpy(&header[263], "00", 2);
@@ -279,7 +287,8 @@ static void traverse_tree(void *buffer, unsigned long size,
                eltbuf = read_sha1_file(sha1, elttype, &eltsize);
                if (!eltbuf)
                        die("cannot read %s", sha1_to_hex(sha1));
-               write_header(sha1, basedir, prefix, path, mode, eltsize);
+               write_header(sha1, S_ISDIR(mode) ? '5' : '0', basedir,
+                            prefix, path, mode, eltsize);
                if (!strcmp(elttype, "tree")) {
                        this_prefix.name = path;
                        traverse_tree(eltbuf, eltsize, &this_prefix);
@@ -320,6 +329,7 @@ time_t commit_time(void * buffer, unsigned long size)
 int main(int argc, char **argv)
 {
        unsigned char sha1[20];
+       unsigned char commit_sha1[20];
        void *buffer;
        unsigned long size;
 
@@ -339,8 +349,9 @@ int main(int argc, char **argv)
        if (!sha1_file_directory)
                sha1_file_directory = DEFAULT_DB_ENVIRONMENT;
 
-       buffer = read_object_with_reference(sha1, "commit", &size, NULL);
+       buffer = read_object_with_reference(sha1, "commit", &size, commit_sha1);
        if (buffer) {
+               write_global_extended_header(commit_sha1);
                archive_time = commit_time(buffer, size);
                free(buffer);
        }
@@ -351,7 +362,7 @@ int main(int argc, char **argv)
        if (!archive_time)
                archive_time = time(NULL);
        if (basedir)
-               write_header("0", NULL, NULL, basedir, 040755, 0);
+               write_header("0", '5', NULL, NULL, basedir, 040755, 0);
        traverse_tree(buffer, size, NULL);
        free(buffer);
        write_trailer();