libarchive: treat one "FIXME: avoid seek"

function                                             old     new   delta
xmalloc_read_with_initial_buf                          -     205    +205
setup_transformer_on_fd                              154     150      -4
xmalloc_open_zipped_read_close                       143     135      -8
xmalloc_read                                         201      10    -191
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/3 up/down: 205/-203)            Total: 2 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 27 insertions, 17 deletions

diff --git a/archival/libarchive/open_transformer.c b/archival/libarchive/open_transformer.c
index 4a4bf3916..97bcc32f0 100644
--- a/archival/libarchive/open_transformer.c
+++ b/archival/libarchive/open_transformer.c
@@ -159,47 +159,44 @@ void FAST_FUNC fork_transformer(int fd, const char *transform_prog)
  */
 static transformer_state_t *setup_transformer_on_fd(int fd, int fail_if_not_compressed)
 {
-        union {
-                uint8_t b[4];
-                uint16_t b16[2];
-                uint32_t b32[1];
-        } magic;
         transformer_state_t *xstate;
 
         xstate = xzalloc(sizeof(*xstate));
         xstate->src_fd = fd;
-        xstate->signature_skipped = 2;
 
         /* .gz and .bz2 both have 2-byte signature, and their
          * unpack_XXX_stream wants this header skipped. */
-        xread(fd, magic.b16, sizeof(magic.b16[0]));
+        xstate->signature_skipped = 2;
+        xread(fd, xstate->magic.b16, 2);
         if (ENABLE_FEATURE_SEAMLESS_GZ
-         && magic.b16[0] == GZIP_MAGIC
+         && xstate->magic.b16[0] == GZIP_MAGIC
         ) {
                 xstate->xformer = unpack_gz_stream;
                 USE_FOR_NOMMU(xstate->xformer_prog = "gunzip";)
                 goto found_magic;
         }
         if (ENABLE_FEATURE_SEAMLESS_Z
-         && magic.b16[0] == COMPRESS_MAGIC
+         && xstate->magic.b16[0] == COMPRESS_MAGIC
         ) {
                 xstate->xformer = unpack_Z_stream;
                 USE_FOR_NOMMU(xstate->xformer_prog = "uncompress";)
                 goto found_magic;
         }
         if (ENABLE_FEATURE_SEAMLESS_BZ2
-         && magic.b16[0] == BZIP2_MAGIC
+         && xstate->magic.b16[0] == BZIP2_MAGIC
         ) {
                 xstate->xformer = unpack_bz2_stream;
                 USE_FOR_NOMMU(xstate->xformer_prog = "bunzip2";)
                 goto found_magic;
         }
         if (ENABLE_FEATURE_SEAMLESS_XZ
-         && magic.b16[0] == XZ_MAGIC1
+         && xstate->magic.b16[0] == XZ_MAGIC1
         ) {
+                uint32_t v32;
                 xstate->signature_skipped = 6;
-                xread(fd, magic.b32, sizeof(magic.b32[0]));
-                if (magic.b32[0] == XZ_MAGIC2) {
+                xread(fd, &xstate->magic.b16[1], 4);
+                move_from_unaligned32(v32, &xstate->magic.b16[1]);
+                if (v32 == XZ_MAGIC2) {
                         xstate->xformer = unpack_xz_stream;
                         USE_FOR_NOMMU(xstate->xformer_prog = "unxz";)
                         goto found_magic;
@@ -344,11 +341,24 @@ void* FAST_FUNC xmalloc_open_zipped_read_close(const char *fname, size_t *maxsz_
                                 *maxsz_p = xstate->mem_output_size;
                 }
         } else {
-                /* File is not compressed */
-//FIXME: avoid seek
-                xlseek(xstate->src_fd, - xstate->signature_skipped, SEEK_CUR);
+                /* File is not compressed.
+                 * We already read first few bytes, account for that.
+                 * Exmaple where it happens:
+                 * "modinfo MODULE.ko" (not compressed)
+                 *   open("MODULE.ko", O_RDONLY|O_LARGEFILE) = 4
+                 *   read(4, "\177E", 2)                     = 2
+                 *   fstat64(4, ...)
+                 *   mmap(...)
+                 *   read(4, "LF\2\1\1\0\0\0\0"...
+                 * ...and we avoided seeking on the fd! :)
+                 */
                 xstate->signature_skipped = 0;
-                image = xmalloc_read(xstate->src_fd, maxsz_p);
+                image = xmalloc_read_with_initial_buf(
+                        xstate->src_fd,
+                        maxsz_p,
+                        xmemdup(&xstate->magic, xstate->signature_skipped),
+                        xstate->signature_skipped
+                );
         }
 
         if (!image)