Re: [PATCH] Add Zstandard support

[Dave Reisner <d@falconindy.com>]

On Tue, Aug 25, 2020 at 10:12:57AM -0700, Lucas De Marchi wrote:
> Hi,
> 
> On Fri, Aug 21, 2020 at 3:46 PM Torge Matthies
> <openglfreak@googlemail.com> wrote:
> >
> > I was not able to find any existing zstd patch for kmod, so I wrote my own.
> 
> thanks a lot for adding this.
> 
> >
> > I was struggling to get the C code below the 80 character line length limit,
> > that's why I used gotos. I used descriptive label names, and it still looks
> > clean enough in my opinion.
> 
> Humn.. I'd rather prefer not to be on 80 chars than using some of the gotos,
> but take a look below
> 
> >
> > I changed the style of the hackargs variable in autogen.sh to multiline
> > because said line was becoming a bit long with the new --with-zstd arg
> > added.
> 
> ok
> 
> >
> > This patch has been running on my two Arch Linux installations (with an
> > accompanying mkinitcpio patch) for several months over many kernel updates
> > without any issues.
> 
> great. Is Arch already using zstd for the kernel? Once this lands, is
> it going to
> zstd for modules?
> 
> +Dave
> 

No plans that I'm aware of. We currently use CONFIG_MODULE_COMPRESS_XZ=y
to have Kbuild do the module compression for us at build time. Is Kbuild
being updated to support zstd if/when this patch lands in a kmod
release?

Personally, I'd rather see less module compression, not more. This
"flavor of the week" compression stuff makes me tired, and the way
compression is implemented in userspace inhibits more important features
like secure module loading via finit_module.

dR

> > Any additional testing and/or patch review would of course be appreciated.
> >
> > Signed-off-by: Torge Matthies <openglfreak@googlemail.com>
> > ---
> >  .semaphore/semaphore.yml     |   4 +-
> >  .travis.yml                  |   1 +
> >  Makefile.am                  |   4 +-
> >  autogen.sh                   |   9 ++-
> >  configure.ac                 |  13 +++-
> >  libkmod/libkmod-file.c       | 119 +++++++++++++++++++++++++++++++++++
> >  libkmod/libkmod.pc.in        |   2 +-
> >  shared/util.c                |   3 +
> >  testsuite/mkosi/mkosi.fedora |   1 +
> >  testsuite/test-util.c        |   3 +
> >  10 files changed, 153 insertions(+), 6 deletions(-)
> >
> > diff --git a/.semaphore/semaphore.yml b/.semaphore/semaphore.yml
> > index db47ca1..fe1d78a 100644
> > --- a/.semaphore/semaphore.yml
> > +++ b/.semaphore/semaphore.yml
> > @@ -22,7 +22,7 @@ blocks:
> >        prologue:
> >          commands:
> >            - sudo apt update
> > -          - sudo apt --yes install docbook-xsl liblzma-dev zlib1g-dev cython linux-headers-generic libssl-dev
> > +          - sudo apt --yes install docbook-xsl libzstd-dev liblzma-dev zlib1g-dev cython linux-headers-generic libssl-dev
> >            - checkout
> >
> >        epilogue:
> > @@ -42,5 +42,5 @@ blocks:
> >        prologue:
> >          commands:
> >            - sudo apt update
> > -          - sudo apt --yes install docbook-xsl liblzma-dev zlib1g-dev cython linux-headers-generic libssl-dev
> > +          - sudo apt --yes install docbook-xsl libzstd-dev liblzma-dev zlib1g-dev cython linux-headers-generic libssl-dev
> >            - checkout
> > diff --git a/.travis.yml b/.travis.yml
> > index 02c753e..0fcce14 100644
> > --- a/.travis.yml
> > +++ b/.travis.yml
> > @@ -14,6 +14,7 @@ matrix:
> >  before_install:
> >    - sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
> >    - sudo apt-get update -qq
> > +  - sudo apt-get install -qq libzstd-dev
> >    - sudo apt-get install -qq liblzma-dev
> >    - sudo apt-get install -qq zlib1g-dev
> >    - sudo apt-get install -qq xsltproc docbook-xsl
> > diff --git a/Makefile.am b/Makefile.am
> > index 8eadb99..37d840b 100644
> > --- a/Makefile.am
> > +++ b/Makefile.am
> > @@ -31,6 +31,8 @@ SED_PROCESS = \
> >         -e 's,@exec_prefix\@,$(exec_prefix),g' \
> >         -e 's,@libdir\@,$(libdir),g' \
> >         -e 's,@includedir\@,$(includedir),g' \
> > +       -e 's,@libzstd_CFLAGS\@,${libzstd_CFLAGS},g' \
> > +       -e 's,@libzstd_LIBS\@,${libzstd_LIBS},g' \
> >         -e 's,@liblzma_CFLAGS\@,${liblzma_CFLAGS},g' \
> >         -e 's,@liblzma_LIBS\@,${liblzma_LIBS},g' \
> >         -e 's,@zlib_CFLAGS\@,${zlib_CFLAGS},g' \
> > @@ -90,7 +92,7 @@ libkmod_libkmod_la_DEPENDENCIES = \
> >         ${top_srcdir}/libkmod/libkmod.sym
> >  libkmod_libkmod_la_LIBADD = \
> >         shared/libshared.la \
> > -       ${liblzma_LIBS} ${zlib_LIBS} ${libcrypto_LIBS}
> > +       ${libzstd_LIBS} ${liblzma_LIBS} ${zlib_LIBS} ${libcrypto_LIBS}
> >
> >  noinst_LTLIBRARIES += libkmod/libkmod-internal.la
> >  libkmod_libkmod_internal_la_SOURCES = $(libkmod_libkmod_la_SOURCES)
> > diff --git a/autogen.sh b/autogen.sh
> > index 67b119f..e4997c4 100755
> > --- a/autogen.sh
> > +++ b/autogen.sh
> > @@ -32,7 +32,14 @@ fi
> >
> >  cd $oldpwd
> >
> > -hackargs="--enable-debug --enable-python --with-xz --with-zlib --with-openssl"
> > +hackargs="\
> > +--enable-debug \
> > +--enable-python \
> > +--with-zstd \
> > +--with-xz \
> > +--with-zlib \
> > +--with-openssl \
> > +"
> >
> >  if [ "x$1" = "xc" ]; then
> >          shift
> > diff --git a/configure.ac b/configure.ac
> > index 4a65d6b..a49f6b9 100644
> > --- a/configure.ac
> > +++ b/configure.ac
> > @@ -83,6 +83,17 @@ AC_ARG_WITH([rootlibdir],
> >          [], [with_rootlibdir=$libdir])
> >  AC_SUBST([rootlibdir], [$with_rootlibdir])
> >
> > +AC_ARG_WITH([zstd],
> > +       AS_HELP_STRING([--with-zstd], [handle Zstandard-compressed modules @<:@default=disabled@:>@]),
> > +       [], [with_zstd=no])
> > +AS_IF([test "x$with_zstd" != "xno"], [
> > +       PKG_CHECK_MODULES([libzstd], [libzstd >= 1.4.4])
> > +       AC_DEFINE([ENABLE_ZSTD], [1], [Enable Zstandard for modules.])
> > +], [
> > +       AC_MSG_NOTICE([Zstandard support not requested])
> > +])
> > +CC_FEATURE_APPEND([with_features], [with_zstd], [ZSTD])
> > +
> >  AC_ARG_WITH([xz],
> >         AS_HELP_STRING([--with-xz], [handle Xz-compressed modules @<:@default=disabled@:>@]),
> >         [], [with_xz=no])
> > @@ -307,7 +318,7 @@ AC_MSG_RESULT([
> >         tools:                  ${enable_tools}
> >         python bindings:        ${enable_python}
> >         logging:                ${enable_logging}
> > -       compression:            xz=${with_xz}  zlib=${with_zlib}
> > +       compression:            zstd=${with_zstd}  xz=${with_xz}  zlib=${with_zlib}
> >         debug:                  ${enable_debug}
> >         coverage:               ${enable_coverage}
> >         doc:                    ${enable_gtk_doc}
> > diff --git a/libkmod/libkmod-file.c b/libkmod/libkmod-file.c
> > index 5eeba6a..1a2e753 100644
> > --- a/libkmod/libkmod-file.c
> > +++ b/libkmod/libkmod-file.c
> > @@ -26,6 +26,9 @@
> >  #include <sys/stat.h>
> >  #include <sys/types.h>
> >  #include <unistd.h>
> > +#ifdef ENABLE_ZSTD
> > +#include <zstd.h>
> > +#endif
> >  #ifdef ENABLE_XZ
> >  #include <lzma.h>
> >  #endif
> > @@ -45,6 +48,9 @@ struct file_ops {
> >  };
> >
> >  struct kmod_file {
> > +#ifdef ENABLE_ZSTD
> > +       bool zstd_used;
> > +#endif
> >  #ifdef ENABLE_XZ
> >         bool xz_used;
> >  #endif
> > @@ -60,6 +66,116 @@ struct kmod_file {
> >         struct kmod_elf *elf;
> >  };
> >
> > +#ifdef ENABLE_ZSTD
> > +static int load_zstd(struct kmod_file *file)
> > +{
> > +       ZSTD_DStream *dstr = NULL;
> > +       size_t in_buf_size, out_buf_min_size, out_buf_size;
> > +       uint8_t *in_buf = NULL, *out_buf = NULL;
> > +       ZSTD_inBuffer zst_input;
> > +       ZSTD_outBuffer zst_output;
> > +       int ret = -EINVAL;
> > +
> > +       dstr = ZSTD_createDStream();
> > +       if (dstr == NULL) {
> > +               ERR(file->ctx, "zstd: Failed to create decompression stream\n");
> > +               ret = -EINVAL;
> > +               goto out;
> > +       }
> > +
> > +       in_buf_size = ZSTD_initDStream(dstr);
> > +       in_buf = malloc(in_buf_size);
> > +       if (in_buf == NULL) {
> > +               ERR(file->ctx, "zstd: %s\n", strerror(ENOMEM));
> 
> no big deal, but malloc() should set errno, so you could use
> ret = -errno before printing and then use %m in the message.
> 
> Same thing in other places.
> 
> > +               ret = -ENOMEM;
> > +               goto out;
> > +       }
> > +
> > +       out_buf_size = out_buf_min_size = ZSTD_DStreamOutSize();
> > +       out_buf = malloc(out_buf_size);
> > +       if (out_buf == NULL) {
> > +               ERR(file->ctx, "zstd: %s\n", strerror(ENOMEM));
> > +               ret = -ENOMEM;
> > +               goto out;
> > +       }
> > +
> > +       zst_input.src = in_buf;
> > +       zst_output.dst = out_buf;
> > +       zst_output.size = out_buf_size;
> > +       zst_output.pos = 0;
> > +       while (true) {
> > +               ssize_t rdret;
> > +               size_t dsret;
> > +               uint8_t *tmp;
> > +
> > +               rdret = read(file->fd, in_buf, in_buf_size);
> > +               if (rdret < 0) {
> > +                       ret = -errno;
> > +                       goto out;
> > +               }
> > +               if (rdret == 0)
> > +                       break;
> > +
> > +               zst_input.size = rdret;
> > +               zst_input.pos = 0;
> > +
> > +               if (zst_output.size - zst_output.pos < out_buf_min_size)
> > +                       goto realloc_buffer;
> 
> this could be a helper function to realloc the buffer. It can even be shared
> for the first alloc if you initialize zst_output.size to 0.. Then you
> have something like:
> 
> > +
> > +try_decompress:
> > +               dsret = ZSTD_decompressStream(dstr, &zst_output, &zst_input);
> > +               if (ZSTD_isError(dsret)) {
> > +                       ERR(file->ctx, "zstd: %s\n", ZSTD_getErrorName(dsret));
> > +                       ret = -EINVAL;
> > +                       goto out;
> > +               }
> > +
> > +               if (zst_output.pos < zst_output.size
> > +                       && zst_output.size - zst_output.pos
> > +                       >= out_buf_min_size) {
> > +                       if (zst_input.pos < zst_input.size)
> > +                               goto try_decompress;
> 
> this looks like a while/for loop. Could even be in a helper function
> 
> 
> > +                       else
> > +                               continue;
> > +               }
> > +
> > +realloc_buffer:
> > +               tmp = realloc(out_buf, out_buf_size + out_buf_min_size);
> > +               if (tmp == NULL) {
> > +                       ret = -errno;
> > +                       goto out;
> > +               }
> > +               out_buf_size += out_buf_min_size;
> > +               out_buf = tmp;
> > +               zst_output.dst = out_buf;
> > +               zst_output.size = out_buf_size;
> > +               goto try_decompress;
> > +       }
> > +
> > +       ZSTD_freeDStream(dstr);
> > +       free(in_buf);
> > +       file->zstd_used = true;
> > +       file->memory = out_buf;
> > +       file->size = zst_output.pos;
> > +       return 0;
> > +out:
> > +       if (dstr != NULL)
> > +               ZSTD_freeDStream(dstr);
> > +       free(out_buf);
> > +       free(in_buf);
> > +       return ret;
> > +}
> > +
> > +static void unload_zstd(struct kmod_file *file)
> > +{
> > +       if (!file->zstd_used)
> > +               return;
> > +       free(file->memory);
> > +}
> > +
> > +static const char magic_zstd[] = {0x28, 0xB5, 0x2F, 0xFD};
> > +#endif
> > +
> >  #ifdef ENABLE_XZ
> >  static void xz_uncompress_belch(struct kmod_file *file, lzma_ret ret)
> >  {
> > @@ -238,6 +354,9 @@ static const struct comp_type {
> >         const char *magic_bytes;
> >         const struct file_ops ops;
> >  } comp_types[] = {
> > +#ifdef ENABLE_ZSTD
> > +       {sizeof(magic_zstd), magic_zstd, {load_zstd, unload_zstd}},
> > +#endif
> >  #ifdef ENABLE_XZ
> >         {sizeof(magic_xz), magic_xz, {load_xz, unload_xz}},
> >  #endif
> > diff --git a/libkmod/libkmod.pc.in b/libkmod/libkmod.pc.in
> > index e4fdf21..3acca6a 100644
> > --- a/libkmod/libkmod.pc.in
> > +++ b/libkmod/libkmod.pc.in
> > @@ -7,5 +7,5 @@ Name: libkmod
> >  Description: Library to deal with kernel modules
> >  Version: @VERSION@
> >  Libs: -L${libdir} -lkmod
> > -Libs.private: @liblzma_LIBS@ @zlib_LIBS@
> > +Libs.private: @libzstd_LIBS@ @liblzma_LIBS@ @zlib_LIBS@
> >  Cflags: -I${includedir}
> > diff --git a/shared/util.c b/shared/util.c
> > index fd2028d..b487b5f 100644
> > --- a/shared/util.c
> > +++ b/shared/util.c
> > @@ -45,6 +45,9 @@ static const struct kmod_ext {
> >  #endif
> >  #ifdef ENABLE_XZ
> >         {".ko.xz", sizeof(".ko.xz") - 1},
> > +#endif
> > +#ifdef ENABLE_ZSTD
> > +       {".ko.zst", sizeof(".ko.zst") - 1},
> >  #endif
> >         { }
> >  };
> > diff --git a/testsuite/mkosi/mkosi.fedora b/testsuite/mkosi/mkosi.fedora
> > index 5252f87..7a2ee5e 100644
> > --- a/testsuite/mkosi/mkosi.fedora
> > +++ b/testsuite/mkosi/mkosi.fedora
> > @@ -19,6 +19,7 @@ BuildPackages =
> >         make
> >         pkgconf-pkg-config
> >         xml-common
> > +       libzstd-devel
> >         xz-devel
> >         zlib-devel
> >         openssl-devel
> > diff --git a/testsuite/test-util.c b/testsuite/test-util.c
> > index 5e25e58..621446b 100644
> > --- a/testsuite/test-util.c
> > +++ b/testsuite/test-util.c
> > @@ -156,6 +156,9 @@ static int test_path_ends_with_kmod_ext(const struct test *t)
> >  #endif
> >  #ifdef ENABLE_XZ
> >                 { "/bla.ko.xz", true },
> > +#endif
> > +#ifdef ENABLE_ZSTD
> > +               { "/bla.ko.zst", true },
> 
> I think we want a zstd-compressed module in the testsuite as well to test this.
> 
> thanks
> Lucas De Marchi
> 
> >  #endif
> >                 { "/bla.ko.x", false },
> >                 { "/bla.ko.", false },
> > --
> > 2.28.0
> >