[Qemu-devel] [PATCH V9 3/4] raw-posix: Add full image preallocation option

[Chen Fan]

From: Hu Tao <address@hidden>

This patch adds a new option preallocation for raw format, and implements
full preallocation by writing zeros to disk.

The metadata option is changed to use posix_fallocate() to ensure
subsquent writes to image file won't fail because of lack of disk space.

The purpose is to ensure disk space for image file. In cases
posix_fallocate() is supported, metadata option can be used, otherwise
(posix_fallocate() is not supported by filesystem, or in case of thin
 provisioning), full option has to be used. User has to choose the proper
way to use.

Signed-off-by: Hu Tao <address@hidden>
---
 block/raw-posix.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 54 insertions(+), 7 deletions(-)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index 710ea9b..07e2088 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -1246,6 +1246,7 @@ static int raw_create(const char *filename, 
QEMUOptionParameter *options,
     int fd;
     int result = 0;
     int64_t total_size = 0;
+    PreallocMode prealloc = PREALLOC_MODE_OFF;
 
     strstart(filename, "file:", &filename);
 
@@ -1254,6 +1255,18 @@ static int raw_create(const char *filename, 
QEMUOptionParameter *options,
         if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
             total_size = (options->value.n + BDRV_SECTOR_SIZE) &
                 BDRV_SECTOR_MASK;
+        } else if (!strcmp(options->name, BLOCK_OPT_PREALLOC)) {
+            if (!options->value.s || !strcmp(options->value.s, "off")) {
+                prealloc = PREALLOC_MODE_OFF;
+            } else if (!strcmp(options->value.s, "metadata")) {
+                prealloc = PREALLOC_MODE_METADATA;
+            } else if (!strcmp(options->value.s, "full")) {
+                prealloc = PREALLOC_MODE_FULL;
+            } else {
+                error_setg(errp, "Invalid preallocation mode: '%s'",
+                           options->value.s);
+                return -EINVAL;
+            }
         }
         options++;
     }
@@ -1263,16 +1276,45 @@ static int raw_create(const char *filename, 
QEMUOptionParameter *options,
     if (fd < 0) {
         result = -errno;
         error_setg_errno(errp, -result, "Could not create file");
-    } else {
-        if (ftruncate(fd, total_size) != 0) {
-            result = -errno;
-            error_setg_errno(errp, -result, "Could not resize file");
+        goto out;
+    }
+    if (ftruncate(fd, total_size) != 0) {
+        result = -errno;
+        error_setg_errno(errp, -result, "Could not resize file");
+        goto out_close;
+    }
+    if (prealloc == PREALLOC_MODE_METADATA) {
+        /* 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");
         }
-        if (qemu_close(fd) != 0) {
-            result = -errno;
-            error_setg_errno(errp, -result, "Could not close the new file");
+    } else if (prealloc == PREALLOC_MODE_FULL) {
+        char *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");
+                g_free(buf);
+                goto out_close;
+            }
+            left -= num;
         }
+        fsync(fd);
+        g_free(buf);
+    }
+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;
 }
 
@@ -1447,6 +1489,11 @@ static QEMUOptionParameter raw_create_options[] = {
         .type = OPT_SIZE,
         .help = "Virtual disk size"
     },
+    {
+        .name = BLOCK_OPT_PREALLOC,
+        .type = OPT_STRING,
+        .help = "Preallocation mode (allowed values: off, metadata, full)"
+    },
     { NULL }
 };
 
-- 
1.9.3