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Nir Soffer

2018-Aug-18 22:13 UTC

[Libguestfs] [PATCH v3 0/4] file: Zero for block devices and older file systems

This version addresses some of the comments on v2.

Changes since v2:
- file_zero: Add missing space in function call
- is_aligned: Assert that align is indeed a power of 2
- Spelling in commit message

Not changed:
- Eric commented that spacing was off:
  https://www.redhat.com/archives/libguestfs/2018-August/msg00113.html
  but I could not find anything wrong.
- Eric asked if ioctl.h will cause grief on BSD compilation:
  https://www.redhat.com/archives/libguestfs/2018-August/msg00116.html
  I tested with FreeBSD 11.0 and 10.3 and there is no issue.
  I also look at NetBSD and OpenBSD source, and in alll ioctl()
  is defined in ioctl.h.

v2 was here:
https://www.redhat.com/archives/libguestfs/2018-August/msg00041.html

Nir Soffer (4):
  file: Avoid unsupported fallocate() calls
  file: Support zero without ZERO_RANGE
  common: Add isaligned helper module
  file: Zero for block devices on old kernels

 common/include/isaligned.h |  51 +++++++++++
 plugins/file/Makefile.am   |   3 +-
 plugins/file/file.c        | 182 +++++++++++++++++++++++++++++--------
 3 files changed, 197 insertions(+), 39 deletions(-)
 create mode 100644 common/include/isaligned.h

-- 
2.17.1

Nir Soffer

2018-Aug-18 22:13 UTC

head link

[Libguestfs] [PATCH v3 1/4] file: Avoid unsupported fallocate() calls

When using file systems not supporting ZERO_RANGE (e.g. NFS 4.2) or
block device on kernel < 4.9, we used to call fallocate() for every
zero, fail with EOPNOTSUPP, and fallback to manual zeroing.  When
trimming, we used to try unsupported fallocate() on every call.

Change file handle to remember if punching holes or zeroing range are
supported, and avoid unsupported calls.

- zero changed to:
  1. If we can punch hole and may trim, try PUNCH_HOLE
  2. If we can zero range, try ZERO_RANGE
  3. Fall back to manual writing

- trim changed to:
  1. If we can punch hole, try PUNCH_HOLE
  2. Succeed
---
 plugins/file/file.c | 80 ++++++++++++++++++++++++++++++---------------
 1 file changed, 53 insertions(+), 27 deletions(-)

diff --git a/plugins/file/file.c b/plugins/file/file.c
index 3bb4d17..5daab63 100644
--- a/plugins/file/file.c
+++ b/plugins/file/file.c
@@ -33,6 +33,7 @@
 
 #include <config.h>
 
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -118,6 +119,8 @@ file_config_complete (void)
 /* The per-connection handle. */
 struct handle {
   int fd;
+  bool can_punch_hole;
+  bool can_zero_range;
 };
 
 /* Create the per-connection handle. */
@@ -146,6 +149,18 @@ file_open (int readonly)
     return NULL;
   }
 
+#ifdef FALLOC_FL_PUNCH_HOLE
+  h->can_punch_hole = true;
+#else
+  h->can_punch_hole = false;
+#endif
+
+#ifdef FALLOC_FL_ZERO_RANGE
+  h->can_zero_range = true;
+#else
+  h->can_zero_range = false;
+#endif
+
   return h;
 }
 
@@ -252,34 +267,42 @@ file_pwrite (void *handle, const void *buf, uint32_t
count, uint64_t offset)
 static int
 file_zero (void *handle, uint32_t count, uint64_t offset, int may_trim)
 {
-#if defined(FALLOC_FL_PUNCH_HOLE) || defined(FALLOC_FL_ZERO_RANGE)
   struct handle *h = handle;
-#endif
   int r = -1;
 
 #ifdef FALLOC_FL_PUNCH_HOLE
-  if (may_trim) {
+  if (h->can_punch_hole && may_trim) {
     r = do_fallocate (h->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
                       offset, count);
-    if (r == -1 && errno != EOPNOTSUPP) {
+    if (r == 0)
+      return r;
+
+    if (errno != EOPNOTSUPP) {
       nbdkit_error ("zero: %m");
+      return r;
     }
-    /* PUNCH_HOLE is older; if it is not supported, it is likely that
-       ZERO_RANGE will not work either, so fall back to write. */
-    return r;
+
+    h->can_punch_hole = false;
   }
 #endif
 
 #ifdef FALLOC_FL_ZERO_RANGE
-  r = do_fallocate (h->fd, FALLOC_FL_ZERO_RANGE, offset, count);
-  if (r == -1 && errno != EOPNOTSUPP) {
-    nbdkit_error ("zero: %m");
+  if (h->can_zero_range) {
+    r = do_fallocate (h->fd, FALLOC_FL_ZERO_RANGE, offset, count);
+    if (r== 0)
+      return r;
+
+    if (errno != EOPNOTSUPP) {
+      nbdkit_error ("zero: %m");
+      return r;
+    }
+
+    h->can_zero_range = false;
   }
-#else
-  /* Trigger a fall back to writing */
-  errno = EOPNOTSUPP;
 #endif
 
+  /* Trigger a fall back to writing */
+  errno = EOPNOTSUPP;
   return r;
 }
 
@@ -301,27 +324,30 @@ file_flush (void *handle)
 static int
 file_trim (void *handle, uint32_t count, uint64_t offset)
 {
-  int r = -1;
 #ifdef FALLOC_FL_PUNCH_HOLE
   struct handle *h = handle;
+  int r = -1;
+
+  if (h->can_punch_hole) {
+    r = do_fallocate (h->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+                      offset, count);
+    if (r == -1) {
+      /* Trim is advisory; we don't care if it fails for anything other
+       * than EIO or EPERM. */
+      if (errno == EPERM || errno == EIO) {
+        nbdkit_error ("fallocate: %m");
+        return r;
+      }
+
+      if (errno == EOPNOTSUPP)
+        h->can_punch_hole = false;
 
-  /* Trim is advisory; we don't care if it fails for anything other
-   * than EIO or EPERM. */
-  r = do_fallocate (h->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
-                    offset, count);
-  if (r < 0) {
-    if (errno != EPERM && errno != EIO) {
       nbdkit_debug ("ignoring failed fallocate during trim: %m");
-      r = 0;
     }
-    else
-      nbdkit_error ("fallocate: %m");
   }
-#else
-  /* Based on .can_trim, this should not be reached. */
-  errno = EOPNOTSUPP;
 #endif
-  return r;
+
+  return 0;
 }
 
 static struct nbdkit_plugin plugin = {
-- 
2.17.1

Nir Soffer

2018-Aug-18 22:13 UTC

head link

[Libguestfs] [PATCH v3 2/4] file: Support zero without ZERO_RANGE

File systems not supporting FALLOC_FL_ZERO_RANGE yet fall back to manual
zeroing.

We can avoid this by combining two fallocate calls:

    fallocate(FALLOC_FL_PUNCH_HOLE)
    fallocate(0)

Based on my tests this is much more efficient compared to manual
zeroing. The idea came from this qemu patch:
https://github.com/qemu/qemu/commit/1cdc3239f1bb

Here is an example run with NFS 4.2 without this change, converting
fedora 27 image created with virt-builder:

$ export SOCK=/tmp/nbd.sock
$ export FILE=/nfs-mount/fedora-27.img
$ src/nbdkit plugins/file/.libs/nbdkit-file-plugin.so file=$FILE -U $SOCK

$ time qemu-img convert -n -f raw -O raw /var/tmp/fedora-27.img
nbd:unix:/tmp/nbd.sock

real	0m17.481s
user	0m0.199s
sys	0m0.691s

$ time qemu-img convert -n -f raw -O raw -W /var/tmp/fedora-27.img
nbd:unix:/tmp/nbd.sock

real	0m17.072s
user	0m0.191s
sys	0m0.738s

With this change:

$ time qemu-img convert -n -f raw -O raw /var/tmp/fedora-27.img
nbd:unix:/tmp/nbd.sock

real	0m6.285s
user	0m0.217s
sys	0m0.829s

$ time qemu-img convert -n -f raw -O raw -W /var/tmp/fedora-27.img
nbd:unix:/tmp/nbd.sock

real	0m3.967s
user	0m0.193s
sys	0m0.702s

Note: the image is sparse, but nbdkit creates a fully allocated image.
This may be a bug in nbdkit or qemu-img.
---
 plugins/file/file.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/plugins/file/file.c b/plugins/file/file.c
index 5daab63..e96aa86 100644
--- a/plugins/file/file.c
+++ b/plugins/file/file.c
@@ -121,6 +121,7 @@ struct handle {
   int fd;
   bool can_punch_hole;
   bool can_zero_range;
+  bool can_fallocate;
 };
 
 /* Create the per-connection handle. */
@@ -161,6 +162,8 @@ file_open (int readonly)
   h->can_zero_range = false;
 #endif
 
+  h->can_fallocate = true;
+
   return h;
 }
 
@@ -301,6 +304,35 @@ file_zero (void *handle, uint32_t count, uint64_t offset,
int may_trim)
   }
 #endif
 
+#ifdef FALLOC_FL_PUNCH_HOLE
+  /* If we can punch hole but may not trim, we can combine punching hole and
+   * fallocate to zero a range. This is expected to be more efficient than
+   * writing zeros manually. */
+  if (h->can_punch_hole && h->can_fallocate) {
+    r = do_fallocate (h->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+                      offset, count);
+    if (r == 0) {
+      r = do_fallocate (h->fd, 0, offset, count);
+      if (r == 0)
+        return r;
+
+      if (errno != EOPNOTSUPP) {
+        nbdkit_error ("zero: %m");
+        return r;
+      }
+
+      h->can_fallocate = false;
+    } else {
+      if (errno != EOPNOTSUPP) {
+        nbdkit_error ("zero: %m");
+        return r;
+      }
+
+      h->can_punch_hole = false;
+    }
+  }
+#endif
+
   /* Trigger a fall back to writing */
   errno = EOPNOTSUPP;
   return r;
-- 
2.17.1

Nir Soffer

2018-Aug-18 22:13 UTC

head link

[Libguestfs] [PATCH v3 3/4] common: Add isaligned helper module

is_aligned (size, align) returns true if size is aligned to align,
assuming that align is power of 2.

Suggested by Eric Blake in
https://www.redhat.com/archives/libguestfs/2018-August/msg00036.html
---
 common/include/isaligned.h | 51 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 common/include/isaligned.h

diff --git a/common/include/isaligned.h b/common/include/isaligned.h
new file mode 100644
index 0000000..e693820
--- /dev/null
+++ b/common/include/isaligned.h
@@ -0,0 +1,51 @@
+/* nbdkit
+ * Copyright (C) 2018 Red Hat Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * * Neither the name of Red Hat nor the names of its contributors may be
+ * used to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS
IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+ * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef NBDKIT_ISALIGNED_H
+#define NBDKIT_ISALIGNED_H
+
+#include <assert.h>
+#include <stdbool.h>
+
+#include "ispowerof2.h"
+
+/* Return true if size is a multiple of align. align must be power of 2.
+ */
+static inline bool
+is_aligned (unsigned int size, unsigned int align)
+{
+  assert (is_power_of_2 (align));
+  return !(size & (align - 1));
+}
+
+#endif /* NBDKIT_ISALIGNED_H */
-- 
2.17.1

Nir Soffer

2018-Aug-18 22:13 UTC

head link

[Libguestfs] [PATCH v3 4/4] file: Zero for block devices on old kernels

fallocate(FALLOC_FL_ZERO_RANGE) is supported for block devices with
modern kernel, but when it is not, we fall back to manual zeroing.

For block device, try also to use ioctl(BLKZEROOUT) if offset and count
are aligned to block device sector size.

Here is an example run without this change on RHEL 7.5:

$ export SOCK=/tmp/nbd.sock
$ export
BLOCK=/dev/e30bfac2-8e13-479d-8cd6-c6da5e306c4e/c9864222-bc52-4359-80d7-76e47d619b15
$ src/nbdkit plugins/file/.libs/nbdkit-file-plugin.so file=$BLOCK -U $SOCK

$ time qemu-img convert -n -f raw -O raw /var/tmp/fedora-27.img
nbd:unix:/tmp/nbd.sock

real	0m11.563s
user	0m0.219s
sys	0m0.746s

$ time qemu-img convert -n -f raw -O raw -W /var/tmp/fedora-27.img
nbd:unix:/tmp/nbd.sock

real	0m9.841s
user	0m0.167s
sys	0m0.715s

With this change:

$ time qemu-img convert -n -f raw -O raw /var/tmp/fedora-27.img
nbd:unix:/tmp/nbd.sock

real	0m2.796s
user	0m0.202s
sys	0m0.700s

$ time qemu-img convert -n -f raw -O raw -W /var/tmp/fedora-27.img
nbd:unix:/tmp/nbd.sock

real	0m1.908s
user	0m0.166s
sys	0m0.728s
---
 plugins/file/Makefile.am |  3 +-
 plugins/file/file.c      | 70 +++++++++++++++++++++++++++++++++-------
 2 files changed, 61 insertions(+), 12 deletions(-)

diff --git a/plugins/file/Makefile.am b/plugins/file/Makefile.am
index 00eaf59..91adbcb 100644
--- a/plugins/file/Makefile.am
+++ b/plugins/file/Makefile.am
@@ -41,7 +41,8 @@ nbdkit_file_plugin_la_SOURCES = \
 	$(top_srcdir)/include/nbdkit-plugin.h
 
 nbdkit_file_plugin_la_CPPFLAGS = \
-	-I$(top_srcdir)/include
+	-I$(top_srcdir)/include \
+	-I$(top_srcdir)/common/include
 nbdkit_file_plugin_la_CFLAGS = \
 	$(WARNINGS_CFLAGS)
 nbdkit_file_plugin_la_LDFLAGS = \
diff --git a/plugins/file/file.c b/plugins/file/file.c
index e96aa86..a0c7b0b 100644
--- a/plugins/file/file.c
+++ b/plugins/file/file.c
@@ -41,14 +41,21 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/ioctl.h>
 #include <errno.h>
 
 #if defined(__linux__) && !defined(FALLOC_FL_PUNCH_HOLE)
 #include <linux/falloc.h>   /* For FALLOC_FL_*, glibc < 2.18 */
 #endif
 
+#if defined(__linux__)
+#include <linux/fs.h>       /* For BLKZEROOUT */
+#endif
+
 #include <nbdkit-plugin.h>
 
+#include "isaligned.h"
+
 #ifndef O_CLOEXEC
 #define O_CLOEXEC 0
 #endif
@@ -119,9 +126,12 @@ file_config_complete (void)
 /* The per-connection handle. */
 struct handle {
   int fd;
+  bool is_block_device;
+  int sector_size;
   bool can_punch_hole;
   bool can_zero_range;
   bool can_fallocate;
+  bool can_zeroout;
 };
 
 /* Create the per-connection handle. */
@@ -129,6 +139,7 @@ static void *
 file_open (int readonly)
 {
   struct handle *h;
+  struct stat statbuf;
   int flags;
 
   h = malloc (sizeof *h);
@@ -150,6 +161,22 @@ file_open (int readonly)
     return NULL;
   }
 
+  if (fstat (h->fd, &statbuf) == -1) {
+    nbdkit_error ("fstat: %s: %m", filename);
+    free (h);
+    return NULL;
+  }
+
+  h->is_block_device = S_ISBLK(statbuf.st_mode);
+  h->sector_size = 4096;  /* Start with safe guess */
+
+#ifdef BLKSSZGET
+  if (h->is_block_device) {
+    if (ioctl (h->fd, BLKSSZGET, &h->sector_size))
+      nbdkit_debug ("cannot get sector size: %s: %m", filename);
+  }
+#endif
+
 #ifdef FALLOC_FL_PUNCH_HOLE
   h->can_punch_hole = true;
 #else
@@ -163,6 +190,7 @@ file_open (int readonly)
 #endif
 
   h->can_fallocate = true;
+  h->can_zeroout = h->is_block_device;
 
   return h;
 }
@@ -184,27 +212,29 @@ static int64_t
 file_get_size (void *handle)
 {
   struct handle *h = handle;
-  struct stat statbuf;
 
-  if (fstat (h->fd, &statbuf) == -1) {
-    nbdkit_error ("stat: %m");
-    return -1;
-  }
-
-  if (S_ISBLK (statbuf.st_mode)) {
+  if (h->is_block_device) {
+    /* Block device, so st_size will not be the true size. */
     off_t size;
 
-    /* Block device, so st_size will not be the true size. */
     size = lseek (h->fd, 0, SEEK_END);
     if (size == -1) {
       nbdkit_error ("lseek (to find device size): %m");
       return -1;
     }
+
     return size;
-  }
+  } else {
+    /* Regular file. */
+    struct stat statbuf;
 
-  /* Else regular file. */
-  return statbuf.st_size;
+    if (fstat (h->fd, &statbuf) == -1) {
+      nbdkit_error ("fstat: %m");
+      return -1;
+    }
+
+    return statbuf.st_size;
+  }
 }
 
 static int
@@ -333,6 +363,24 @@ file_zero (void *handle, uint32_t count, uint64_t offset,
int may_trim)
   }
 #endif
 
+#ifdef BLKZEROOUT
+  /* For aligned range and block device, we can use BLKZEROOUT. */
+  if (h->can_zeroout && is_aligned (offset | count,
h->sector_size)) {
+    uint64_t range[2] = {offset, count};
+
+    r = ioctl (h->fd, BLKZEROOUT, &range);
+    if (r == 0)
+      return r;
+
+    if (errno != ENOTTY) {
+      nbdkit_error ("zero: %m");
+      return r;
+    }
+
+    h->can_zeroout = false;
+  }
+#endif
+
   /* Trigger a fall back to writing */
   errno = EOPNOTSUPP;
   return r;
-- 
2.17.1

Richard W.M. Jones

2018-Aug-19 11:35 UTC

head link

Re: [Libguestfs] [PATCH v3 1/4] file: Avoid unsupported fallocate() calls

On Sun, Aug 19, 2018 at 01:13:05AM +0300, Nir Soffer
wrote:> When using file systems not supporting ZERO_RANGE (e.g. NFS 4.2) or
> block device on kernel < 4.9, we used to call fallocate() for every
> zero, fail with EOPNOTSUPP, and fallback to manual zeroing.  When
> trimming, we used to try unsupported fallocate() on every call.
> 
> Change file handle to remember if punching holes or zeroing range are
> supported, and avoid unsupported calls.
> 
> - zero changed to:
>   1. If we can punch hole and may trim, try PUNCH_HOLE
>   2. If we can zero range, try ZERO_RANGE
>   3. Fall back to manual writing
> 
> - trim changed to:
>   1. If we can punch hole, try PUNCH_HOLE
>   2. Succeed
> ---
>  plugins/file/file.c | 80 ++++++++++++++++++++++++++++++---------------
>  1 file changed, 53 insertions(+), 27 deletions(-)
> 
> diff --git a/plugins/file/file.c b/plugins/file/file.c
> index 3bb4d17..5daab63 100644
> --- a/plugins/file/file.c
> +++ b/plugins/file/file.c
> @@ -33,6 +33,7 @@
>  
>  #include <config.h>
>  
> +#include <stdbool.h>
>  #include <stdio.h>
>  #include <stdlib.h>
Can you put stdbook after stdlib for consistency with the
other source files.
>  #ifdef FALLOC_FL_ZERO_RANGE
> -  r = do_fallocate (h->fd, FALLOC_FL_ZERO_RANGE, offset, count);
> -  if (r == -1 && errno != EOPNOTSUPP) {
> -    nbdkit_error ("zero: %m");
> +  if (h->can_zero_range) {
> +    r = do_fallocate (h->fd, FALLOC_FL_ZERO_RANGE, offset, count);
> +    if (r== 0)
Spacing.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html

Richard W.M. Jones

2018-Aug-19 11:38 UTC

head link

Re: [Libguestfs] [PATCH v3 1/4] file: Avoid unsupported fallocate() calls

On Sun, Aug 19, 2018 at 01:13:05AM +0300, Nir Soffer
wrote:> -    if (r == -1 && errno != EOPNOTSUPP) {
> +    if (r == 0)
> +      return r;
> +
> +    if (errno != EOPNOTSUPP) {
>        nbdkit_error ("zero: %m");
> +      return r;
I think these cases where we "return r" are rather awkward
(there are more of them in this commit).

I think we should return 0 or return -1 as appropriate.  It seems
clearer to me and has less risk of going wrong in future
if we rearrange the code.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html

Richard W.M. Jones

2018-Aug-19 11:39 UTC

head link

Re: [Libguestfs] [PATCH v3 3/4] common: Add isaligned helper module

On Sun, Aug 19, 2018 at 01:13:07AM +0300, Nir Soffer
wrote:> is_aligned (size, align) returns true if size is aligned to align,
> assuming that align is power of 2.
> 
> Suggested by Eric Blake in
> https://www.redhat.com/archives/libguestfs/2018-August/msg00036.html
> ---
>  common/include/isaligned.h | 51 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 51 insertions(+)
>  create mode 100644 common/include/isaligned.h
> 
> diff --git a/common/include/isaligned.h b/common/include/isaligned.h
You have to add this file to common/include/Makefile.am otherwise
it will never be distributed.

Rich.
> new file mode 100644
> index 0000000..e693820
> --- /dev/null
> +++ b/common/include/isaligned.h
> @@ -0,0 +1,51 @@
> +/* nbdkit
> + * Copyright (C) 2018 Red Hat Inc.
> + * All rights reserved.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions are
> + * met:
> + *
> + * * Redistributions of source code must retain the above copyright
> + * notice, this list of conditions and the following disclaimer.
> + *
> + * * Redistributions in binary form must reproduce the above copyright
> + * notice, this list of conditions and the following disclaimer in the
> + * documentation and/or other materials provided with the distribution.
> + *
> + * * Neither the name of Red Hat nor the names of its contributors may be
> + * used to endorse or promote products derived from this software without
> + * specific prior written permission.
> + *
> + * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS
IS'' AND
> + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
> + * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
> + * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
> + * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
> + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
> + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
> + * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
> + * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
> + * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
> + * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
> + * SUCH DAMAGE.
> + */
> +
> +#ifndef NBDKIT_ISALIGNED_H
> +#define NBDKIT_ISALIGNED_H
> +
> +#include <assert.h>
> +#include <stdbool.h>
> +
> +#include "ispowerof2.h"
> +
> +/* Return true if size is a multiple of align. align must be power of 2.
> + */
> +static inline bool
> +is_aligned (unsigned int size, unsigned int align)
> +{
> +  assert (is_power_of_2 (align));
> +  return !(size & (align - 1));
> +}
> +
> +#endif /* NBDKIT_ISALIGNED_H */
> -- 
> 2.17.1
-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org

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