[PATCH 1/4] io: Implement zstdio decompression

* [PATCH 1/4] io: Implement zstdio decompression
  2025-09-23 20:12 [PATCH 0/4] Add zstdio support for booting Trixie kernels in Xen Logan Gunthorpe via Grub-devel
@ 2025-09-23 20:12 ` Logan Gunthorpe via Grub-devel
  0 siblings, 0 replies; 9+ messages in thread
From: Logan Gunthorpe via Grub-devel @ 2025-09-23 20:12 UTC (permalink / raw)
  To: grub-devel, Daniel Kiper, Alex Burmashev,
	Vladimir 'phcoder' Serbinenko
  Cc: Logan Gunthorpe, Nagy Elemér Károly

Add zstd based io decompression.

Based largely on the existing xzio, implement the same features using
the zstd library already included in the project.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 Makefile.util.def           |   1 +
 grub-core/Makefile.core.def |   9 +-
 grub-core/io/zstdio.c       | 237 ++++++++++++++++++++++++++++++++++++
 include/grub/file.h         |   3 +-
 4 files changed, 248 insertions(+), 2 deletions(-)
 create mode 100644 grub-core/io/zstdio.c

diff --git a/Makefile.util.def b/Makefile.util.def
index 038253b37a42..74786177f908 100644
--- a/Makefile.util.def
+++ b/Makefile.util.def
@@ -162,6 +162,7 @@ library = {
   common = grub-core/io/gzio.c;
   common = grub-core/io/xzio.c;
   common = grub-core/io/lzopio.c;
+  common = grub-core/io/zstdio.c;
   common = grub-core/kern/ia64/dl_helper.c;
   common = grub-core/kern/arm/dl_helper.c;
   common = grub-core/kern/arm64/dl_helper.c;
diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index 0fcf67f9df7d..4c8005782e31 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -473,7 +473,7 @@ image = {
   i386_pc = boot/i386/pc/boot.S;
 
   cppflags = '-DHYBRID_BOOT=1';
-  
+
   i386_pc_ldflags = '$(TARGET_IMG_LDFLAGS)';
   i386_pc_ldflags = '$(TARGET_IMG_BASE_LDOPT),0x7C00';
 
@@ -2486,6 +2486,13 @@ module = {
   cppflags = '-I$(srcdir)/lib/posix_wrap -I$(srcdir)/lib/minilzo -DMINILZO_HAVE_CONFIG_H';
 };
 
+module = {
+  name = zstdio;
+  common = io/zstdio.c;
+  cppflags = '-I$(srcdir)/lib/posix_wrap -I$(srcdir)/lib/zstd';
+  cflags='-Wno-unreachable-code';
+};
+
 module = {
   name = testload;
   common = commands/testload.c;
diff --git a/grub-core/io/zstdio.c b/grub-core/io/zstdio.c
new file mode 100644
index 000000000000..b64655aa63e3
--- /dev/null
+++ b/grub-core/io/zstdio.c
@@ -0,0 +1,237 @@
+/* zstdio.c - decompression support for zstd */
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2010  Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <grub/err.h>
+#include <grub/mm.h>
+#include <grub/misc.h>
+#include <grub/file.h>
+#include <grub/fs.h>
+#include <grub/dl.h>
+
+GRUB_MOD_LICENSE ("GPLv3+");
+
+#include "zstd.h"
+
+#define STREAM_HEADER_SIZE 16
+
+struct grub_zstdio
+{
+  grub_file_t file;
+  ZSTD_DCtx *dctx;
+  grub_size_t insize;
+  grub_size_t outsize;
+
+  ZSTD_outBuffer output;
+  ZSTD_inBuffer input;
+
+  grub_off_t saved_offset;
+  grub_uint8_t bufs[];
+};
+
+typedef struct grub_zstdio *grub_zstdio_t;
+static struct grub_fs grub_zstdio_fs;
+
+static int
+test_header (grub_file_t file)
+{
+  grub_zstdio_t zstdio = file->data;
+  size_t zret;
+
+  zstdio->input.pos = 0;
+  zstdio->output.pos = 0;
+  zstdio->output.size = zstdio->outsize;
+  zstdio->input.size = grub_file_read (zstdio->file, zstdio->bufs,
+				       STREAM_HEADER_SIZE);
+  if (zstdio->input.size != STREAM_HEADER_SIZE)
+    return 0;
+
+  zret = ZSTD_decompressStream(zstdio->dctx, &zstdio->output, &zstdio->input);
+  if (ZSTD_isError(zret))
+    return 0;
+
+  return 1;
+}
+
+static grub_file_t
+grub_zstdio_open (grub_file_t io, enum grub_file_type type)
+{
+  grub_file_t file;
+  grub_zstdio_t zstdio;
+
+  if (type & GRUB_FILE_TYPE_NO_DECOMPRESS)
+    return io;
+
+  file = (grub_file_t) grub_zalloc (sizeof (*file));
+  if (!file)
+    return 0;
+
+  zstdio = grub_zalloc (sizeof (*zstdio) + ZSTD_DStreamInSize() +
+			ZSTD_DStreamOutSize());
+  if (!zstdio)
+    {
+      grub_free (file);
+      return 0;
+    }
+
+  zstdio->file = io;
+  zstdio->insize = ZSTD_DStreamInSize();
+  zstdio->outsize = ZSTD_DStreamOutSize();
+  zstdio->input.src = zstdio->bufs;
+  zstdio->output.dst = &zstdio->bufs[zstdio->insize];
+
+  file->device = io->device;
+  file->data = zstdio;
+  file->fs = &grub_zstdio_fs;
+  file->size = GRUB_FILE_SIZE_UNKNOWN;
+  file->not_easily_seekable = 1;
+
+  if (grub_file_tell (zstdio->file) != 0)
+    grub_file_seek (zstdio->file, 0);
+
+  zstdio->dctx = ZSTD_createDCtx();
+  if (!zstdio->dctx)
+    {
+      grub_free (file);
+      grub_free (zstdio);
+      return 0;
+    }
+
+  if (!test_header (file))
+    {
+      grub_errno = GRUB_ERR_NONE;
+      grub_file_seek (io, 0);
+      ZSTD_freeDCtx(zstdio->dctx);
+      grub_free (zstdio);
+      grub_free (file);
+
+      return io;
+    }
+
+  return file;
+}
+
+static grub_ssize_t
+grub_zstdio_read (grub_file_t file, char *buf, grub_size_t len)
+{
+  grub_zstdio_t zstdio = file->data;
+  grub_ssize_t ret = 0;
+  grub_ssize_t readret;
+  grub_off_t current_offset;
+  grub_size_t zret;
+
+  /* If seek backward need to reset decoder and start from beginning of file. */
+  if (file->offset < zstdio->saved_offset)
+    {
+      ZSTD_initDStream(zstdio->dctx);
+      zstdio->input.pos = 0;
+      zstdio->input.size = 0;
+      zstdio->output.pos = 0;
+      zstdio->saved_offset = 0;
+      grub_file_seek (zstdio->file, 0);
+    }
+
+  current_offset = zstdio->saved_offset;
+
+  while (len > 0)
+    {
+      zstdio->output.size = file->offset + ret + len - current_offset;
+      if (zstdio->output.size > zstdio->outsize)
+	zstdio->output.size = zstdio->outsize;
+      if (zstdio->input.pos == zstdio->input.size)
+	{
+	  readret = grub_file_read (zstdio->file, zstdio->bufs,
+				    zstdio->insize);
+	  if (readret < 0)
+	    return -1;
+	  zstdio->input.size = readret;
+	  zstdio->input.pos = 0;
+	}
+
+      zret = ZSTD_decompressStream(zstdio->dctx, &zstdio->output,
+				   &zstdio->input);
+      if (ZSTD_isError(zret))
+	{
+	  grub_error (GRUB_ERR_BAD_COMPRESSED_DATA,
+		      N_("zstd file corrupted or unsupported block options"));
+	  return -1;
+        }
+
+      grub_off_t new_offset = current_offset + zstdio->output.pos;
+
+      if (file->offset <= new_offset)
+	  /* Store first chunk of data in buffer.  */
+        {
+	  grub_size_t delta = new_offset - (file->offset + ret);
+	  grub_memmove (buf, (grub_uint8_t *)zstdio->output.dst +
+			(zstdio->output.pos - delta),
+	                delta);
+	  len -= delta;
+	  buf += delta;
+	  ret += delta;
+	}
+	current_offset = new_offset;
+
+	zstdio->output.pos = 0;
+
+	if (zstdio->input.pos == 0 && zstdio->output.pos == 0)
+	  break;
+    }
+
+  if (ret >= 0)
+    zstdio->saved_offset = file->offset + ret;
+
+  return ret;
+}
+
+/* Release everything, including the underlying file object.  */
+static grub_err_t
+grub_zstdio_close (grub_file_t file)
+{
+  grub_zstdio_t zstdio = file->data;
+
+  ZSTD_freeDCtx(zstdio->dctx);
+
+  grub_file_close (zstdio->file);
+  grub_free (zstdio);
+
+  /* Device must not be closed twice.  */
+  file->device = 0;
+  file->name = 0;
+  return grub_errno;
+}
+
+static struct grub_fs grub_zstdio_fs = {
+  .name = "zstdio",
+  .fs_dir = 0,
+  .fs_open = 0,
+  .fs_read = grub_zstdio_read,
+  .fs_close = grub_zstdio_close,
+  .fs_label = 0,
+  .next = 0
+};
+
+GRUB_MOD_INIT (zstdio)
+{
+  grub_file_filter_register (GRUB_FILE_FILTER_ZSTDIO, grub_zstdio_open);
+}
+
+GRUB_MOD_FINI (zstdio)
+{
+  grub_file_filter_unregister (GRUB_FILE_FILTER_ZSTDIO);
+}
diff --git a/include/grub/file.h b/include/grub/file.h
index a5bf3a792d6f..7c665730a090 100644
--- a/include/grub/file.h
+++ b/include/grub/file.h
@@ -186,9 +186,10 @@ typedef enum grub_file_filter_id
     GRUB_FILE_FILTER_GZIO,
     GRUB_FILE_FILTER_XZIO,
     GRUB_FILE_FILTER_LZOPIO,
+    GRUB_FILE_FILTER_ZSTDIO,
     GRUB_FILE_FILTER_MAX,
     GRUB_FILE_FILTER_COMPRESSION_FIRST = GRUB_FILE_FILTER_GZIO,
-    GRUB_FILE_FILTER_COMPRESSION_LAST = GRUB_FILE_FILTER_LZOPIO,
+    GRUB_FILE_FILTER_COMPRESSION_LAST = GRUB_FILE_FILTER_ZSTDIO,
   } grub_file_filter_id_t;
 
 typedef grub_file_t (*grub_file_filter_t) (grub_file_t in, enum grub_file_type type);
-- 
2.47.3


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