Add utility functions to read the fragment data from an image

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

2 files changed, 181 insertions, 1 deletions

diff --git a/lib/Makemodule.am b/lib/Makemodule.am
index 3b171c6..f23d9b7 100644
--- a/lib/Makemodule.am
+++ b/lib/Makemodule.am
@@ -14,7 +14,8 @@ libsquashfs_a_SOURCES += lib/sqfs/table.c include/table.h
 libsquashfs_a_SOURCES += lib/sqfs/read_super.c lib/sqfs/meta_reader.c
 libsquashfs_a_SOURCES += include/meta_reader.h lib/sqfs/id_table_write.c
 libsquashfs_a_SOURCES += lib/sqfs/id_table_read.c lib/sqfs/read_inode.c
-libsquashfs_a_SOURCES += lib/sqfs/readdir.c
+libsquashfs_a_SOURCES += lib/sqfs/readdir.c lib/sqfs/frag_reader.c
+libsquashfs_a_SOURCES += include/frag_reader.h
 
 libutil_a_SOURCES = lib/util/canonicalize_name.c lib/util/write_retry.c
 libutil_a_SOURCES += lib/util/read_retry.c include/util.h
diff --git a/lib/sqfs/frag_reader.c b/lib/sqfs/frag_reader.c
new file mode 100644
index 0000000..1906376
--- /dev/null
+++ b/lib/sqfs/frag_reader.c
@@ -0,0 +1,179 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+#include "meta_reader.h"
+#include "frag_reader.h"
+#include "util.h"
+
+#include <unistd.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+static int precache_block(frag_reader_t *f, size_t i)
+{
+	bool compressed;
+	size_t size;
+	ssize_t ret;
+
+	if (i == f->current_index)
+		return 0;
+
+	if (lseek(f->fd, f->tbl[i].start_offset, SEEK_SET) == (off_t)-1) {
+		perror("seeking to fragment location");
+		return -1;
+	}
+
+	compressed = (f->tbl[i].size & (1 << 24)) == 0;
+	size = f->tbl[i].size & ((1 << 24) - 1);
+
+	if (size > f->block_size) {
+		fputs("found fragment block larger than block size\n", stderr);
+		return -1;
+	}
+
+	ret = read_retry(f->fd, f->buffer, size);
+	if (ret < 0) {
+		perror("reading fragment");
+		return -1;
+	}
+
+	if ((size_t)ret < size) {
+		fputs("reading fragment: unexpected end of file\n", stderr);
+		return -1;
+	}
+
+	if (compressed) {
+		ret = f->cmp->do_block(f->cmp, f->buffer, size);
+
+		if (ret <= 0) {
+			fputs("extracting fragment failed\n", stderr);
+			return -1;
+		}
+	}
+
+	f->current_index = i;
+	f->used = ret;
+	return 0;
+}
+
+
+frag_reader_t *frag_reader_create(sqfs_super_t *super, int fd,
+				  compressor_t *cmp)
+{
+	size_t i, blockcount, j, diff, count;
+	sqfs_fragment_t *tbl = NULL;
+	uint64_t *locations = NULL;
+	meta_reader_t *m = NULL;
+	frag_reader_t *f = NULL;
+	ssize_t ret;
+
+	count = super->fragment_entry_count;
+	blockcount = count / (SQFS_META_BLOCK_SIZE / sizeof(tbl[0]));
+
+	if (count % (SQFS_META_BLOCK_SIZE / sizeof(tbl[0])))
+		++blockcount;
+
+	/* pre allocate all the stuff */
+	f = calloc(1, sizeof(*f) + super->block_size);
+	if (f == NULL)
+		goto fail_rd;
+
+	tbl = malloc(count * sizeof(tbl[0]));
+	if (tbl == NULL)
+		goto fail_rd;
+
+	locations = malloc(blockcount * sizeof(locations[0]));
+	if (locations == NULL)
+		goto fail_rd;
+
+	/* read the meta block offset table */
+	if (lseek(fd, super->fragment_table_start, SEEK_SET) == (off_t)-1)
+		goto fail_seek;
+
+	ret = read_retry(fd, locations, blockcount * sizeof(locations[0]));
+	if (ret < 0)
+		goto fail_rd;
+
+	if ((size_t)ret < (blockcount * sizeof(locations[0])))
+		goto fail_trunc;
+
+	for (i = 0; i < blockcount; ++i)
+		locations[i] = le64toh(locations[i]);
+
+	/* read the meta blocks */
+	m = meta_reader_create(fd, cmp);
+	if (m == NULL)
+		goto fail;
+
+	for (i = 0, j = 0; i < blockcount && j < count; ++i, j += diff) {
+		if (meta_reader_seek(m, locations[i], 0))
+			goto fail;
+
+		diff = SQFS_META_BLOCK_SIZE / sizeof(tbl[0]);
+		if (diff > count)
+			diff = count;
+
+		if (meta_reader_read(m, tbl + j, diff * sizeof(tbl[0])))
+			goto fail;
+	}
+
+	for (i = 0; i < count; ++i) {
+		tbl[i].start_offset = le64toh(tbl[i].start_offset);
+		tbl[i].size = le32toh(tbl[i].size);
+	}
+
+	/* cleanup and ship it */
+	meta_reader_destroy(m);
+	free(locations);
+
+	f->tbl = tbl;
+	f->num_fragments = count;
+	f->cmp = cmp;
+	f->fd = fd;
+	f->block_size = super->block_size;
+	f->current_index = count;
+	return f;
+fail_seek:
+	perror("seek to fragment table");
+	goto fail;
+fail_trunc:
+	fputs("reading fragment table: unexpected end of file\n", stderr);
+	goto fail;
+fail_rd:
+	perror("reading fragment table");
+	goto fail;
+fail:
+	if (m != NULL)
+		meta_reader_destroy(m);
+	free(tbl);
+	free(locations);
+	free(f);
+	return NULL;
+}
+
+void frag_reader_destroy(frag_reader_t *f)
+{
+	free(f->tbl);
+	free(f);
+}
+
+int frag_reader_read(frag_reader_t *f, size_t index, size_t offset,
+		     void *buffer, size_t size)
+{
+	if (precache_block(f, index))
+		return -1;
+
+	if (offset >= f->used)
+		goto fail_range;
+
+	if (size == 0)
+		return 0;
+
+	if ((offset + size - 1) >= f->used)
+		goto fail_range;
+
+	memcpy(buffer, f->buffer + offset, size);
+	return 0;
+fail_range:
+	fputs("attempted to read past fragment block limits\n", stderr);
+	return -1;
+}