raw-posix: Add falloc and full preallocation option

This patch adds a new option preallocation for raw format, and implements
falloc and full preallocation.

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/raw-posix.c

@@ -30,6 +30,7 @@
 #include "block/thread-pool.h"
 #include "qemu/iov.h"
 #include "raw-aio.h"
+#include "qapi/util.h"
 
 #if defined(__APPLE__) && (__MACH__)
 #include <paths.h>
@@ -1365,6 +1366,9 @@ static int raw_create(const char *filename, QemuOpts *opts, Error **errp)
     int result = 0;
     int64_t total_size = 0;
     bool nocow = false;
+    PreallocMode prealloc;
+    char *buf = NULL;
+    Error *local_err = NULL;
 
     strstart(filename, "file:", &filename);
 
@@ -1372,13 +1376,25 @@ static int raw_create(const char *filename, QemuOpts *opts, Error **errp)
     total_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
                           BDRV_SECTOR_SIZE);
     nocow = qemu_opt_get_bool(opts, BLOCK_OPT_NOCOW, false);
+    buf = qemu_opt_get_del(opts, BLOCK_OPT_PREALLOC);
+    prealloc = qapi_enum_parse(PreallocMode_lookup, buf,
+                               PREALLOC_MODE_MAX, PREALLOC_MODE_OFF,
+                               &local_err);
+    g_free(buf);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        result = -EINVAL;
+        goto out;
+    }
 
     fd = qemu_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
                    0644);
     if (fd < 0) {
         result = -errno;
         error_setg_errno(errp, -result, "Could not create file");
-    } else {
+        goto out;
+    }
+
     if (nocow) {
 #ifdef __linux__
         /* Set NOCOW flag to solve performance issue on fs like btrfs.
@@ -1397,12 +1413,45 @@ static int raw_create(const char *filename, QemuOpts *opts, Error **errp)
     if (ftruncate(fd, total_size) != 0) {
         result = -errno;
         error_setg_errno(errp, -result, "Could not resize file");
+        goto out_close;
     }
-        if (qemu_close(fd) != 0) {
+
+    if (prealloc == PREALLOC_MODE_FALLOC) {
+        /* posix_fallocate() doesn't set errno. */
+        result = -posix_fallocate(fd, 0, total_size);
+        if (result != 0) {
+            error_setg_errno(errp, -result,
+                             "Could not preallocate data for the new file");
+        }
+    } else if (prealloc == PREALLOC_MODE_FULL) {
+        buf = g_malloc0(65536);
+        int64_t num = 0, left = total_size;
+
+        while (left > 0) {
+            num = MIN(left, 65536);
+            result = write(fd, buf, num);
+            if (result < 0) {
+                result = -errno;
+                error_setg_errno(errp, -result,
+                                 "Could not write to the new file");
+                break;
+            }
+            left -= num;
+        }
+        fsync(fd);
+        g_free(buf);
+    } else if (prealloc != PREALLOC_MODE_OFF) {
+        result = -EINVAL;
+        error_setg(errp, "Unsupported preallocation mode: %s",
+                   PreallocMode_lookup[prealloc]);
+    }
+
+out_close:
+    if (qemu_close(fd) != 0 && result == 0) {
         result = -errno;
         error_setg_errno(errp, -result, "Could not close the new file");
     }
-    }
+out:
     return result;
 }
 
@@ -1585,6 +1634,11 @@ static QemuOptsList raw_create_opts = {
             .type = QEMU_OPT_BOOL,
             .help = "Turn off copy-on-write (valid only on btrfs)"
         },
+        {
+            .name = BLOCK_OPT_PREALLOC,
+            .type = QEMU_OPT_STRING,
+            .help = "Preallocation mode (allowed values: off, falloc, full)"
+        },
         { /* end of list */ }
     }
 };

qemu-doc.texi

@@ -527,6 +527,15 @@ Linux or NTFS on Windows), then only the written sectors will reserve
 space. Use @code{qemu-img info} to know the real size used by the
 image or @code{ls -ls} on Unix/Linux.
 
+Supported options:
+@table @code
+@item preallocation
+Preallocation mode (allowed values: @code{off}, @code{falloc}, @code{full}).
+@code{falloc} mode preallocates space for image by calling posix_fallocate().
+@code{full} mode preallocates space for image by writing zeros to underlying
+storage.
+@end table
+
 @item qcow2
 QEMU image format, the most versatile format. Use it to have smaller
 images (useful if your filesystem does not supports holes, for example

qemu-img.texi

@@ -419,6 +419,15 @@ Linux or NTFS on Windows), then only the written sectors will reserve
 space. Use @code{qemu-img info} to know the real size used by the
 image or @code{ls -ls} on Unix/Linux.
 
+Supported options:
+@table @code
+@item preallocation
+Preallocation mode (allowed values: @code{off}, @code{falloc}, @code{full}).
+@code{falloc} mode preallocates space for image by calling posix_fallocate().
+@code{full} mode preallocates space for image by writing zeros to underlying
+storage.
+@end table
+
 @item qcow2
 QEMU image format, the most versatile format. Use it to have smaller
 images (useful if your filesystem does not supports holes, for example