Implement seeking to earlier offsets in gzipfs. This allows my loader

to e.g. correctly load all .ko.gz's I've tried, as opposed to messing
up trying to read section headers on some of them.

1 files changed, 30 insertions, 15 deletions

diff --git a/lib/libstand/gzipfs.c b/lib/libstand/gzipfs.c
index 02195d8..9cc9ad9 100644
--- a/lib/libstand/gzipfs.c
+++ b/lib/libstand/gzipfs.c
@@ -38,6 +38,7 @@ __FBSDID("$FreeBSD$");
 struct z_file
 {
     int			zf_rawfd;
+    off_t		zf_dataoffset;
     z_stream		zf_zstream;
     char		zf_buf[Z_BUFSIZE];
 };
@@ -98,11 +99,12 @@ zf_fill(struct z_file *zf)
  * Returns 0 if the header is OK, nonzero if not.
  */
 static int
-get_byte(struct z_file *zf)
+get_byte(struct z_file *zf, off_t *curoffp)
 {
     if ((zf->zf_zstream.avail_in == 0) && (zf_fill(zf) == -1))
 	return(-1);
     zf->zf_zstream.avail_in--;
+    ++*curoffp;
     return(*(zf->zf_zstream.next_in)++);
 }
 
@@ -124,36 +126,37 @@ check_header(struct z_file *zf)
     uInt	len;
     int		c;
 
+    zf->zf_dataoffset = 0;
     /* Check the gzip magic header */
     for (len = 0; len < 2; len++) {
-	c = get_byte(zf);
+	c = get_byte(zf, &zf->zf_dataoffset);
 	if (c != gz_magic[len]) {
 	    return(1);
 	}
     }
-    method = get_byte(zf);
-    flags = get_byte(zf);
+    method = get_byte(zf, &zf->zf_dataoffset);
+    flags = get_byte(zf, &zf->zf_dataoffset);
     if (method != Z_DEFLATED || (flags & RESERVED) != 0) {
 	return(1);
     }
     
     /* Discard time, xflags and OS code: */
-    for (len = 0; len < 6; len++) (void)get_byte(zf);
+    for (len = 0; len < 6; len++) (void)get_byte(zf, &zf->zf_dataoffset);
 
     if ((flags & EXTRA_FIELD) != 0) { /* skip the extra field */
-	len  =  (uInt)get_byte(zf);
-	len += ((uInt)get_byte(zf))<<8;
+	len  =  (uInt)get_byte(zf, &zf->zf_dataoffset);
+	len += ((uInt)get_byte(zf, &zf->zf_dataoffset))<<8;
 	/* len is garbage if EOF but the loop below will quit anyway */
-	while (len-- != 0 && get_byte(zf) != -1) ;
+	while (len-- != 0 && get_byte(zf, &zf->zf_dataoffset) != -1) ;
     }
     if ((flags & ORIG_NAME) != 0) { /* skip the original file name */
-	while ((c = get_byte(zf)) != 0 && c != -1) ;
+	while ((c = get_byte(zf, &zf->zf_dataoffset)) != 0 && c != -1) ;
     }
     if ((flags & COMMENT) != 0) {   /* skip the .gz file comment */
-	while ((c = get_byte(zf)) != 0 && c != -1) ;
+	while ((c = get_byte(zf, &zf->zf_dataoffset)) != 0 && c != -1) ;
     }
     if ((flags & HEAD_CRC) != 0) {  /* skip the header crc */
-	for (len = 0; len < 2; len++) c = get_byte(zf);
+	for (len = 0; len < 2; len++) c = get_byte(zf, &zf->zf_dataoffset);
     }
     /* if there's data left, we're in business */
     return((c == -1) ? 1 : 0);
@@ -274,6 +277,20 @@ zf_read(struct open_file *f, void *buf, size_t size, size_t *resid)
     return(0);
 }
 
+static int
+zf_rewind(struct open_file *f)
+{
+    struct z_file	*zf = (struct z_file *)f->f_fsdata;
+
+    if (lseek(zf->zf_rawfd, zf->zf_dataoffset, SEEK_SET) == -1)
+	return -1;
+    zf->zf_zstream.avail_in = 0;
+    zf->zf_zstream.next_in = NULL;
+    (void)inflateReset(&zf->zf_zstream);
+
+    return 0;
+}
+
 static off_t
 zf_seek(struct open_file *f, off_t offset, int where)
 {
@@ -292,11 +309,9 @@ zf_seek(struct open_file *f, off_t offset, int where)
 	target = -1;
     }
 
-    /* Can we get there from here? */
-    if (target < zf->zf_zstream.total_out) {
-	errno = EOFFSET;
+    /* rewind if required */
+    if (target < zf->zf_zstream.total_out && zf_rewind(f) != 0)
 	return -1;
-    } 
 
     /* skip forwards if required */
     while (target > zf->zf_zstream.total_out) {