[PATCH v2 0/3] fetch the alignment of device dax

[PATCH v2 0/3] fetch the alignment of device dax

[Jingqi Liu]

This series adds libdaxctl support and fetchs the alignment of
device dax through libdaxctl [1] APIs.

QEMU uses mmap(2) to maps vNVDIMM backends and aligns the mapping
address to the page size (getpagesize(2)) by default. However, some
types of backends may require an alignment different than the page
size. The 'align' option is provided to memory-backend-file to allow
users to specify the proper alignment.

For device dax (e.g., /dev/dax0.0), the 'align' option needs to
match the alignment requirement of the device dax, which can be fetched
through the libdaxctl APIs.

[1] Libdaxctl is a part of ndctl project.
The project's repository is: https://github.com/pmem/ndctl

Changelog:
  v2: Per Paolo and Dan suggestions, fetch the alignment of device dax
      through libdaxctl APIs.

  v1: The initial version.
      Fetch the alignment through "/sys/dev/char/%d:%d/device/align".

Jingqi Liu (3):
  exec: fetch the alignment of Linux devdax pmem character device nodes
  docs/nvdimm: add description of alignment requirement of device dax
  configure: add libdaxctl support

 configure       | 30 +++++++++++++++++++++++++++
 docs/nvdimm.txt |  9 +++++++++
 exec.c          | 54 ++++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 92 insertions(+), 1 deletion(-)

-- 
2.17.1

[PATCH v2 1/3] exec: fetch the alignment of Linux devdax pmem character device nodes

[Jingqi Liu]

If the backend file is devdax pmem character device, the alignment
specified by the option 'align=NUM' in the '-object memory-backend-file'
needs to match the alignment requirement of the devdax pmem character device.

This patch uses the interfaces of libdaxctl to fetch the devdax pmem file
'align', so that we can compare it with the NUM of 'align=NUM'.
The NUM needs to be larger than or equal to the devdax pmem file 'align'.

It also fixes the problem that mmap() returns failure in qemu_ram_mmap()
when the NUM of 'align=NUM' is less than the devdax pmem file 'align'.

Suggested-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
---
 exec.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/exec.c b/exec.c
index de9d949902..2c3444e47e 100644
--- a/exec.c
+++ b/exec.c
@@ -77,6 +77,10 @@
 
 #include "monitor/monitor.h"
 
+#ifdef CONFIG_LIBDAXCTL
+#include <daxctl/libdaxctl.h>
+#endif
+
 //#define DEBUG_SUBPAGE
 
 #if !defined(CONFIG_USER_ONLY)
@@ -1736,6 +1740,46 @@ static int64_t get_file_size(int fd)
     return size;
 }
 
+static int64_t get_file_align(int fd)
+{
+    int64_t align = -1;
+#if defined(__linux__) && defined(CONFIG_LIBDAXCTL)
+    struct stat st;
+
+    if (fstat(fd, &st) < 0) {
+        return -errno;
+    }
+
+    /* Special handling for devdax character devices */
+    if (S_ISCHR(st.st_mode)) {
+        g_autofree char *path = NULL;
+        g_autofree char *rpath = NULL;
+        struct daxctl_ctx *ctx;
+        struct daxctl_region *region;
+        int rc = 0;
+
+        path = g_strdup_printf("/sys/dev/char/%d:%d",
+                    major(st.st_rdev), minor(st.st_rdev));
+        rpath = realpath(path, NULL);
+
+        rc = daxctl_new(&ctx);
+        if (rc) {
+            return -1;
+        }
+
+        daxctl_region_foreach(ctx, region) {
+            if (strstr(rpath, daxctl_region_get_path(region))) {
+                align = daxctl_region_get_align(region);
+                break;
+            }
+        }
+        daxctl_unref(ctx);
+    }
+#endif /* defined(__linux__) && defined(CONFIG_LIBDAXCTL) */
+
+    return align;
+}
+
 static int file_ram_open(const char *path,
                          const char *region_name,
                          bool *created,
@@ -2275,7 +2319,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
 {
     RAMBlock *new_block;
     Error *local_err = NULL;
-    int64_t file_size;
+    int64_t file_size, file_align;
 
     /* Just support these ram flags by now. */
     assert((ram_flags & ~(RAM_SHARED | RAM_PMEM)) == 0);
@@ -2311,6 +2355,14 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
         return NULL;
     }
 
+    file_align = get_file_align(fd);
+    if (file_align > 0 && mr && file_align > mr->align) {
+        error_setg(errp, "backing store align 0x%" PRIx64
+                   " is larger than 'align' option 0x" RAM_ADDR_FMT,
+                   file_align, mr->align);
+        return NULL;
+    }
+
     new_block = g_malloc0(sizeof(*new_block));
     new_block->mr = mr;
     new_block->used_length = size;
-- 
2.17.1

[PATCH v2 2/3] docs/nvdimm: add description of alignment requirement of device dax

[Jingqi Liu]

For device dax (e.g., /dev/dax0.0), the NUM of 'align=NUM' option
needs to match the alignment requirement of the device dax.
It must be larger than or equal to the 'align' of device dax.

Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
---
 docs/nvdimm.txt | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
index 362e99109e..3c7b6dab5f 100644
--- a/docs/nvdimm.txt
+++ b/docs/nvdimm.txt
@@ -132,6 +132,15 @@ address to the page size (getpagesize(2)) by default. However, some
 types of backends may require an alignment different than the page
 size. In that case, QEMU v2.12.0 and later provide 'align' option to
 memory-backend-file to allow users to specify the proper alignment.
+For device dax (e.g., /dev/dax0.0), this alignment needs to match the
+alignment requirement of the device dax. The NUM of 'align=NUM' option
+must be larger than or equal to the 'align' of device dax.
+We can use the following command to show the 'align' of device dax.
+
+    ndctl list -X
+
+In order to get the proper 'align' of device dax, you need to install
+the library 'libdaxctl'.
 
 For example, device dax require the 2 MB alignment, so we can use
 following QEMU command line options to use it (/dev/dax0.0) as the
-- 
2.17.1

[PATCH v2 3/3] configure: add libdaxctl support

[Jingqi Liu]

Add a pair of configure options --{enable,disable}-libdaxctl to control
whether QEMU is compiled with libdaxctl [1]. Libdaxctl is a utility
library for managing the device dax subsystem.

QEMU uses mmap(2) to maps vNVDIMM backends and aligns the mapping
address to the page size (getpagesize(2)) by default. However, some
types of backends may require an alignment different than the page
size. The 'align' option is provided to memory-backend-file to allow
users to specify the proper alignment.

For device dax (e.g., /dev/dax0.0), the 'align' option needs to match
the alignment requirement of the device dax, which can be fetched
through the libdaxctl APIs.

[1] Libdaxctl is a part of ndctl project.
The project's repository is: https://github.com/pmem/ndctl

For more information about libdaxctl APIs, you can refer to the
comments in source code of: pmem/ndctl/daxctl/lib/libdaxctl.c.

Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
---
 configure | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/configure b/configure
index e225a1e3ff..df1752cf08 100755
--- a/configure
+++ b/configure
@@ -509,6 +509,7 @@ libpmem=""
 default_devices="yes"
 plugins="no"
 fuzzing="no"
+libdaxctl=""
 
 supported_cpu="no"
 supported_os="no"
@@ -1601,6 +1602,10 @@ for opt do
   ;;
   --gdb=*) gdb_bin="$optarg"
   ;;
+  --enable-libdaxctl) libdaxctl=yes
+  ;;
+  --disable-libdaxctl) libdaxctl=no
+  ;;
   *)
       echo "ERROR: unknown option $opt"
       echo "Try '$0 --help' for more information"
@@ -1894,6 +1899,7 @@ disabled with --disable-FEATURE, default is enabled if available:
   debug-mutex     mutex debugging support
   libpmem         libpmem support
   xkbcommon       xkbcommon support
+  libdaxctl       libdaxctl support
 
 NOTE: The object files are built at the place where configure is launched
 EOF
@@ -6190,6 +6196,25 @@ if test "$libpmem" != "no"; then
 	fi
 fi
 
+##########################################
+# check for libdaxctl
+
+if test "$libdaxctl" != "no"; then
+	if $pkg_config --exists "libdaxctl"; then
+		libdaxctl="yes"
+		libdaxctl_libs=$($pkg_config --libs libdaxctl)
+		libdaxctl_cflags=$($pkg_config --cflags libdaxctl)
+		libs_softmmu="$libs_softmmu $libdaxctl_libs"
+		QEMU_CFLAGS="$QEMU_CFLAGS $libdaxctl_cflags"
+	else
+		if test "$libdaxctl" = "yes" ; then
+			feature_not_found "libdaxctl" "Install libdaxctl"
+		fi
+		libdaxctl="no"
+	fi
+fi
+
+
 ##########################################
 # check for slirp
 
@@ -6767,6 +6792,7 @@ echo "parallels support $parallels"
 echo "sheepdog support  $sheepdog"
 echo "capstone          $capstone"
 echo "libpmem support   $libpmem"
+echo "libdaxctl support $libdaxctl"
 echo "libudev           $libudev"
 echo "default devices   $default_devices"
 echo "plugin support    $plugins"
@@ -7590,6 +7616,10 @@ if test "$libpmem" = "yes" ; then
   echo "CONFIG_LIBPMEM=y" >> $config_host_mak
 fi
 
+if test "$libdaxctl" = "yes" ; then
+  echo "CONFIG_LIBDAXCTL=y" >> $config_host_mak
+fi
+
 if test "$bochs" = "yes" ; then
   echo "CONFIG_BOCHS=y" >> $config_host_mak
 fi
-- 
2.17.1

Re: [PATCH v2 0/3] fetch the alignment of device dax

[Liu, Jingqi]

Ping for comments.

Hi Paolo, Dan, Joao,
Any comments for this series.

Thanks,
Jingqi

On 4/15/2020 11:35 AM, Liu, Jingqi wrote:
> This series adds libdaxctl support and fetchs the alignment of
> device dax through libdaxctl [1] APIs.
>
> QEMU uses mmap(2) to maps vNVDIMM backends and aligns the mapping
> address to the page size (getpagesize(2)) by default. However, some
> types of backends may require an alignment different than the page
> size. The 'align' option is provided to memory-backend-file to allow
> users to specify the proper alignment.
>
> For device dax (e.g., /dev/dax0.0), the 'align' option needs to
> match the alignment requirement of the device dax, which can be fetched
> through the libdaxctl APIs.
>
> [1] Libdaxctl is a part of ndctl project.
> The project's repository is: https://github.com/pmem/ndctl
>
> Changelog:
>    v2: Per Paolo and Dan suggestions, fetch the alignment of device dax
>        through libdaxctl APIs.
>
>    v1: The initial version.
>        Fetch the alignment through "/sys/dev/char/%d:%d/device/align".
>
> Jingqi Liu (3):
>    exec: fetch the alignment of Linux devdax pmem character device nodes
>    docs/nvdimm: add description of alignment requirement of device dax
>    configure: add libdaxctl support
>
>   configure       | 30 +++++++++++++++++++++++++++
>   docs/nvdimm.txt |  9 +++++++++
>   exec.c          | 54 ++++++++++++++++++++++++++++++++++++++++++++++++-
>   3 files changed, 92 insertions(+), 1 deletion(-)
>

Re: [PATCH v2 1/3] exec: fetch the alignment of Linux devdax pmem character device nodes

[Joao Martins]

On 4/15/20 4:35 AM, Jingqi Liu wrote:
> If the backend file is devdax pmem character device, the alignment
> specified by the option 'align=NUM' in the '-object memory-backend-file'
> needs to match the alignment requirement of the devdax pmem character device.
> 
> This patch uses the interfaces of libdaxctl to fetch the devdax pmem file
> 'align', so that we can compare it with the NUM of 'align=NUM'.
> The NUM needs to be larger than or equal to the devdax pmem file 'align'.
> 
> It also fixes the problem that mmap() returns failure in qemu_ram_mmap()
> when the NUM of 'align=NUM' is less than the devdax pmem file 'align'.
> 
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>

  Reviewed-by: Joao Martins <joao.m.martins@oracle.com>

I also no longer see the previous problem we talked in v1 wrt to ABI differences
between dax_pmem_compat (your case) vs dax_pmem|dax_hmem (my case). The @align
validation also occurs as expected.

> ---
>  exec.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 53 insertions(+), 1 deletion(-)
> 
> diff --git a/exec.c b/exec.c
> index de9d949902..2c3444e47e 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -77,6 +77,10 @@
>  
>  #include "monitor/monitor.h"
>  
> +#ifdef CONFIG_LIBDAXCTL
> +#include <daxctl/libdaxctl.h>
> +#endif
> +
>  //#define DEBUG_SUBPAGE
>  
>  #if !defined(CONFIG_USER_ONLY)
> @@ -1736,6 +1740,46 @@ static int64_t get_file_size(int fd)
>      return size;
>  }
>  
> +static int64_t get_file_align(int fd)
> +{
> +    int64_t align = -1;
> +#if defined(__linux__) && defined(CONFIG_LIBDAXCTL)
> +    struct stat st;
> +
> +    if (fstat(fd, &st) < 0) {
> +        return -errno;
> +    }
> +
> +    /* Special handling for devdax character devices */
> +    if (S_ISCHR(st.st_mode)) {
> +        g_autofree char *path = NULL;
> +        g_autofree char *rpath = NULL;
> +        struct daxctl_ctx *ctx;
> +        struct daxctl_region *region;
> +        int rc = 0;
> +
> +        path = g_strdup_printf("/sys/dev/char/%d:%d",
> +                    major(st.st_rdev), minor(st.st_rdev));
> +        rpath = realpath(path, NULL);
> +
> +        rc = daxctl_new(&ctx);
> +        if (rc) {
> +            return -1;
> +        }
> +
> +        daxctl_region_foreach(ctx, region) {
> +            if (strstr(rpath, daxctl_region_get_path(region))) {
> +                align = daxctl_region_get_align(region);
> +                break;
> +            }
> +        }
> +        daxctl_unref(ctx);
> +    }
> +#endif /* defined(__linux__) && defined(CONFIG_LIBDAXCTL) */
> +
> +    return align;
> +}
> +
>  static int file_ram_open(const char *path,
>                           const char *region_name,
>                           bool *created,
> @@ -2275,7 +2319,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
>  {
>      RAMBlock *new_block;
>      Error *local_err = NULL;
> -    int64_t file_size;
> +    int64_t file_size, file_align;
>  
>      /* Just support these ram flags by now. */
>      assert((ram_flags & ~(RAM_SHARED | RAM_PMEM)) == 0);
> @@ -2311,6 +2355,14 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
>          return NULL;
>      }
>  
> +    file_align = get_file_align(fd);
> +    if (file_align > 0 && mr && file_align > mr->align) {
> +        error_setg(errp, "backing store align 0x%" PRIx64
> +                   " is larger than 'align' option 0x" RAM_ADDR_FMT,
> +                   file_align, mr->align);
> +        return NULL;
> +    }
> +
>      new_block = g_malloc0(sizeof(*new_block));
>      new_block->mr = mr;
>      new_block->used_length = size;
> 

Re: [PATCH v2 2/3] docs/nvdimm: add description of alignment requirement of device dax

[Joao Martins]

On 4/15/20 4:35 AM, Jingqi Liu wrote:
> For device dax (e.g., /dev/dax0.0), the NUM of 'align=NUM' option
> needs to match the alignment requirement of the device dax.
> It must be larger than or equal to the 'align' of device dax.
> 
> Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
> ---
>  docs/nvdimm.txt | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
> index 362e99109e..3c7b6dab5f 100644
> --- a/docs/nvdimm.txt
> +++ b/docs/nvdimm.txt
> @@ -132,6 +132,15 @@ address to the page size (getpagesize(2)) by default. However, some
>  types of backends may require an alignment different than the page
>  size. In that case, QEMU v2.12.0 and later provide 'align' option to
>  memory-backend-file to allow users to specify the proper alignment.
> +For device dax (e.g., /dev/dax0.0), this alignment needs to match the
> +alignment requirement of the device dax. The NUM of 'align=NUM' option
> +must be larger than or equal to the 'align' of device dax.
> +We can use the following command to show the 'align' of device dax.
> +
> +    ndctl list -X
> +
> +In order to get the proper 'align' of device dax, you need to install
> +the library 'libdaxctl'.
>  
>  For example, device dax require the 2 MB alignment, so we can use
>  following QEMU command line options to use it (/dev/dax0.0) as the
> 

Given that this series introduces support for libdaxctl, perhaps suggesting in
the docs how you can also query the @align with daxctl tool? e.g.

"We can one of the following commands to show the 'align' of device dax:

     ndctl list -X
     daxctl list -R"

The unlikely reason being that users may only install daxctl-{,libs,devel} and
not ndctl-*. It also covers other users like ACPI HMAT/hmem which are not
instrumented with ndctl.

With that:

  Reviewed-by: Joao Martins <joao.m.martins@oracle.com>

	Joao

Re: [PATCH v2 3/3] configure: add libdaxctl support

[Joao Martins]

On 4/15/20 4:35 AM, Jingqi Liu wrote:
> Add a pair of configure options --{enable,disable}-libdaxctl to control
> whether QEMU is compiled with libdaxctl [1]. Libdaxctl is a utility
> library for managing the device dax subsystem.
> 
> QEMU uses mmap(2) to maps vNVDIMM backends and aligns the mapping
> address to the page size (getpagesize(2)) by default. However, some
> types of backends may require an alignment different than the page
> size. The 'align' option is provided to memory-backend-file to allow
> users to specify the proper alignment.
> 
> For device dax (e.g., /dev/dax0.0), the 'align' option needs to match
> the alignment requirement of the device dax, which can be fetched
> through the libdaxctl APIs.
> 
> [1] Libdaxctl is a part of ndctl project.
> The project's repository is: https://github.com/pmem/ndctl
> 
> For more information about libdaxctl APIs, you can refer to the
> comments in source code of: pmem/ndctl/daxctl/lib/libdaxctl.c.
> 
> Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
> ---
>  configure | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/configure b/configure
> index e225a1e3ff..df1752cf08 100755
> --- a/configure
> +++ b/configure
> @@ -509,6 +509,7 @@ libpmem=""
>  default_devices="yes"
>  plugins="no"
>  fuzzing="no"
> +libdaxctl=""
>  
>  supported_cpu="no"
>  supported_os="no"
> @@ -1601,6 +1602,10 @@ for opt do
>    ;;
>    --gdb=*) gdb_bin="$optarg"
>    ;;
> +  --enable-libdaxctl) libdaxctl=yes
> +  ;;
> +  --disable-libdaxctl) libdaxctl=no
> +  ;;
>    *)
>        echo "ERROR: unknown option $opt"
>        echo "Try '$0 --help' for more information"
> @@ -1894,6 +1899,7 @@ disabled with --disable-FEATURE, default is enabled if available:
>    debug-mutex     mutex debugging support
>    libpmem         libpmem support
>    xkbcommon       xkbcommon support
> +  libdaxctl       libdaxctl support
>  
>  NOTE: The object files are built at the place where configure is launched
>  EOF
> @@ -6190,6 +6196,25 @@ if test "$libpmem" != "no"; then
>  	fi
>  fi
>  
> +##########################################
> +# check for libdaxctl
> +
> +if test "$libdaxctl" != "no"; then
> +	if $pkg_config --exists "libdaxctl"; then
> +		libdaxctl="yes"
> +		libdaxctl_libs=$($pkg_config --libs libdaxctl)
> +		libdaxctl_cflags=$($pkg_config --cflags libdaxctl)
> +		libs_softmmu="$libs_softmmu $libdaxctl_libs"
> +		QEMU_CFLAGS="$QEMU_CFLAGS $libdaxctl_cflags"
> +	else
> +		if test "$libdaxctl" = "yes" ; then
> +			feature_not_found "libdaxctl" "Install libdaxctl"
> +		fi

Region iteration APIs, align and path getter routines are only available since
libdaxctl v56/v57 (the latest is v68).

Not sure how likely this happens in today's distros but if we care about systems
with < v57 we should probably check that
daxctl_region_foreach/daxctl_region_get_align/daxctl_region_get_path symbols
exist? Or alternatively requiring v57 or up which serves as a bandage, but more
long term ... any usage of newer daxctl APIs will require the former.

> +		libdaxctl="no"
> +	fi
> +fi
> +
> +
>  ##########################################
>  # check for slirp
>  
> @@ -6767,6 +6792,7 @@ echo "parallels support $parallels"
>  echo "sheepdog support  $sheepdog"
>  echo "capstone          $capstone"
>  echo "libpmem support   $libpmem"
> +echo "libdaxctl support $libdaxctl"
>  echo "libudev           $libudev"
>  echo "default devices   $default_devices"
>  echo "plugin support    $plugins"
> @@ -7590,6 +7616,10 @@ if test "$libpmem" = "yes" ; then
>    echo "CONFIG_LIBPMEM=y" >> $config_host_mak
>  fi
>  
> +if test "$libdaxctl" = "yes" ; then
> +  echo "CONFIG_LIBDAXCTL=y" >> $config_host_mak
> +fi
> +
>  if test "$bochs" = "yes" ; then
>    echo "CONFIG_BOCHS=y" >> $config_host_mak
>  fi
> 

Re: [PATCH v2 2/3] docs/nvdimm: add description of alignment requirement of device dax

[Liu, Jingqi]

[-- Attachment #1: Type: text/plain, Size: 2067 bytes --]

On 4/29/2020 12:22 AM, Joao Martins wrote:
> On 4/15/20 4:35 AM, Jingqi Liu wrote:
>> For device dax (e.g., /dev/dax0.0), the NUM of 'align=NUM' option
>> needs to match the alignment requirement of the device dax.
>> It must be larger than or equal to the 'align' of device dax.
>>
>> Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
>> ---
>>   docs/nvdimm.txt | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
>> index 362e99109e..3c7b6dab5f 100644
>> --- a/docs/nvdimm.txt
>> +++ b/docs/nvdimm.txt
>> @@ -132,6 +132,15 @@ address to the page size (getpagesize(2)) by default. However, some
>>   types of backends may require an alignment different than the page
>>   size. In that case, QEMU v2.12.0 and later provide 'align' option to
>>   memory-backend-file to allow users to specify the proper alignment.
>> +For device dax (e.g., /dev/dax0.0), this alignment needs to match the
>> +alignment requirement of the device dax. The NUM of 'align=NUM' option
>> +must be larger than or equal to the 'align' of device dax.
>> +We can use the following command to show the 'align' of device dax.
>> +
>> +    ndctl list -X
>> +
>> +In order to get the proper 'align' of device dax, you need to install
>> +the library 'libdaxctl'.
>>   
>>   For example, device dax require the 2 MB alignment, so we can use
>>   following QEMU command line options to use it (/dev/dax0.0) as the
>>
> Given that this series introduces support for libdaxctl, perhaps suggesting in
> the docs how you can also query the @align with daxctl tool? e.g.
>
> "We can one of the following commands to show the 'align' of device dax:
>
>       ndctl list -X
>       daxctl list -R"

Thanks for your comments.
I'll add "daxctl list -R" in this doc.

Jingqi

> The unlikely reason being that users may only install daxctl-{,libs,devel} and
> not ndctl-*. It also covers other users like ACPI HMAT/hmem which are not
> instrumented with ndctl.
>
> With that:
>
>    Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
>
> 	Joao

Thanks.


[-- Attachment #2: Type: text/html, Size: 2939 bytes --]

Re: [PATCH v2 3/3] configure: add libdaxctl support

[Liu, Jingqi]

[-- Attachment #1: Type: text/plain, Size: 3364 bytes --]

On 4/29/2020 12:23 AM, Joao Martins wrote:
> On 4/15/20 4:35 AM, Jingqi Liu wrote:
>> Add a pair of configure options --{enable,disable}-libdaxctl to control
>> whether QEMU is compiled with libdaxctl [1]. Libdaxctl is a utility
>> library for managing the device dax subsystem.
>>
>> QEMU uses mmap(2) to maps vNVDIMM backends and aligns the mapping
>> address to the page size (getpagesize(2)) by default. However, some
>> types of backends may require an alignment different than the page
>> size. The 'align' option is provided to memory-backend-file to allow
>> users to specify the proper alignment.
>>
>> For device dax (e.g., /dev/dax0.0), the 'align' option needs to match
>> the alignment requirement of the device dax, which can be fetched
>> through the libdaxctl APIs.
>>
>> [1] Libdaxctl is a part of ndctl project.
>> The project's repository is: https://github.com/pmem/ndctl
>>
>> For more information about libdaxctl APIs, you can refer to the
>> comments in source code of: pmem/ndctl/daxctl/lib/libdaxctl.c.
>>
>> Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
>> ---
>>   configure | 30 ++++++++++++++++++++++++++++++
>>   1 file changed, 30 insertions(+)
>>
>> diff --git a/configure b/configure
>> index e225a1e3ff..df1752cf08 100755
>> --- a/configure
>> +++ b/configure
>> @@ -509,6 +509,7 @@ libpmem=""
>>   default_devices="yes"
>>   plugins="no"
>>   fuzzing="no"
>> +libdaxctl=""
>>   
>>   supported_cpu="no"
>>   supported_os="no"
>> @@ -1601,6 +1602,10 @@ for opt do
>>     ;;
>>     --gdb=*) gdb_bin="$optarg"
>>     ;;
>> +  --enable-libdaxctl) libdaxctl=yes
>> +  ;;
>> +  --disable-libdaxctl) libdaxctl=no
>> +  ;;
>>     *)
>>         echo "ERROR: unknown option $opt"
>>         echo "Try '$0 --help' for more information"
>> @@ -1894,6 +1899,7 @@ disabled with --disable-FEATURE, default is enabled if available:
>>     debug-mutex     mutex debugging support
>>     libpmem         libpmem support
>>     xkbcommon       xkbcommon support
>> +  libdaxctl       libdaxctl support
>>   
>>   NOTE: The object files are built at the place where configure is launched
>>   EOF
>> @@ -6190,6 +6196,25 @@ if test "$libpmem" != "no"; then
>>   	fi
>>   fi
>>   
>> +##########################################
>> +# check for libdaxctl
>> +
>> +if test "$libdaxctl" != "no"; then
>> +	if $pkg_config --exists "libdaxctl"; then
>> +		libdaxctl="yes"
>> +		libdaxctl_libs=$($pkg_config --libs libdaxctl)
>> +		libdaxctl_cflags=$($pkg_config --cflags libdaxctl)
>> +		libs_softmmu="$libs_softmmu $libdaxctl_libs"
>> +		QEMU_CFLAGS="$QEMU_CFLAGS $libdaxctl_cflags"
>> +	else
>> +		if test "$libdaxctl" = "yes" ; then
>> +			feature_not_found "libdaxctl" "Install libdaxctl"
>> +		fi
> Region iteration APIs, align and path getter routines are only available since
> libdaxctl v56/v57 (the latest is v68).
>
> Not sure how likely this happens in today's distros but if we care about systems
> with < v57 we should probably check that
> daxctl_region_foreach/daxctl_region_get_align/daxctl_region_get_path symbols
> exist? Or alternatively requiring v57 or up which serves as a bandage, but more
> long term ... any usage of newer daxctl APIs will require the former.

Thanks for your suggestion.
Better to require v57 or up.
How about adding the following check:
+       if $pkg_config --atleast-version=57 "libdaxctl"; then


Jingqi


[-- Attachment #2: Type: text/html, Size: 3767 bytes --]