[Qemu-devel] [PATCH 3/7] block: raw-posix image file reopen

[Jeff Cody]

This is derived from the Supriya Kannery's reopen patches.

This contains the raw-posix driver changes for the bdrv_reopen_*
functions.  All changes are staged into a temporary scratch buffer
during the prepare() stage, and copied over to the live structure
during commit().  Upon abort(), all changes are abandoned, and the
live structures are unmodified.

The _prepare() will create an extra fd - either by means of a dup,
if possible, or opening a new fd if not (for instance, access
control changes).  Upon _commit(), the original fd is closed and
the new fd is used.  Upon _abort(), the duplicate/new fd is closed.

Signed-off-by: Jeff Cody <address@hidden>
---
 block/raw-posix.c | 153 +++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 139 insertions(+), 14 deletions(-)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index 6be20b1..48086d7 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -140,6 +140,15 @@ typedef struct BDRVRawState {
 #endif
 } BDRVRawState;
 
+typedef struct BDRVRawReopenState {
+    BDRVReopenState reopen_state;
+    int fd;
+    int open_flags;
+    uint8_t *aligned_buf;
+    unsigned aligned_buf_size;
+    BDRVRawState *stash_s;
+} BDRVRawReopenState;
+
 static int fd_open(BlockDriverState *bs);
 static int64_t raw_getlength(BlockDriverState *bs);
 
@@ -185,6 +194,28 @@ static int raw_normalize_devicepath(const char **filename)
 }
 #endif
 
+static void raw_parse_flags(int bdrv_flags, int *open_flags)
+{
+    assert(open_flags != NULL);
+
+    *open_flags |= O_BINARY;
+    *open_flags &= ~O_ACCMODE;
+    if (bdrv_flags & BDRV_O_RDWR) {
+        *open_flags |= O_RDWR;
+    } else {
+        *open_flags |= O_RDONLY;
+    }
+
+    /* Use O_DSYNC for write-through caching, no flags for write-back caching,
+     * and O_DIRECT for no caching. */
+    if ((bdrv_flags & BDRV_O_NOCACHE)) {
+        *open_flags |= O_DIRECT;
+    }
+    if (!(bdrv_flags & BDRV_O_CACHE_WB)) {
+        *open_flags |= O_DSYNC;
+    }
+}
+
 static int raw_open_common(BlockDriverState *bs, const char *filename,
                            int bdrv_flags, int open_flags)
 {
@@ -196,20 +227,8 @@ static int raw_open_common(BlockDriverState *bs, const 
char *filename,
         return ret;
     }
 
-    s->open_flags = open_flags | O_BINARY;
-    s->open_flags &= ~O_ACCMODE;
-    if (bdrv_flags & BDRV_O_RDWR) {
-        s->open_flags |= O_RDWR;
-    } else {
-        s->open_flags |= O_RDONLY;
-    }
-
-    /* Use O_DSYNC for write-through caching, no flags for write-back caching,
-     * and O_DIRECT for no caching. */
-    if ((bdrv_flags & BDRV_O_NOCACHE))
-        s->open_flags |= O_DIRECT;
-    if (!(bdrv_flags & BDRV_O_CACHE_WB))
-        s->open_flags |= O_DSYNC;
+    s->open_flags = open_flags;
+    raw_parse_flags(bdrv_flags, &s->open_flags);
 
     s->fd = -1;
     fd = qemu_open(filename, s->open_flags, 0644);
@@ -283,6 +302,109 @@ static int raw_open(BlockDriverState *bs, const char 
*filename, int flags)
     return raw_open_common(bs, filename, flags, 0);
 }
 
+static int raw_reopen_prepare(BDRVReopenState *state, Error **errp)
+{
+    BDRVRawState *s;
+    BDRVRawReopenState *raw_s;
+    int ret = 0;
+
+    assert(state != NULL);
+    assert(state->bs != NULL);
+
+    s = state->bs->opaque;
+
+    state->opaque = g_malloc0(sizeof(BDRVRawReopenState));
+    raw_s = state->opaque;
+
+    raw_parse_flags(state->flags, &raw_s->open_flags);
+
+    /*
+     * If we didn't have BDRV_O_NOCACHE set before, we may not have allocated
+     * aligned_buf
+     */
+    if ((state->flags & BDRV_O_NOCACHE)) {
+        /*
+         * Allocate a buffer for read/modify/write cycles.  Choose the size
+         * pessimistically as we don't know the block size yet.
+         */
+        raw_s->aligned_buf_size = 32 * MAX_BLOCKSIZE;
+        raw_s->aligned_buf = qemu_memalign(MAX_BLOCKSIZE,
+                                           raw_s->aligned_buf_size);
+
+        if (raw_s->aligned_buf == NULL) {
+            ret = -1;
+            goto error;
+        }
+    }
+
+    int fcntl_flags = O_APPEND | O_ASYNC | O_NONBLOCK;
+#ifdef O_NOATIME
+    fcntl_flags |= O_NOATIME;
+#endif
+    if ((raw_s->open_flags & ~fcntl_flags) == (s->open_flags & ~fcntl_flags)) {
+        /* dup the original fd */
+        /* TODO: use qemu fcntl wrapper */
+        raw_s->fd = fcntl(s->fd, F_DUPFD_CLOEXEC, 0);
+        if (raw_s->fd == -1) {
+            ret = -1;
+            goto error;
+        }
+        ret = fcntl_setfl(raw_s->fd, raw_s->open_flags);
+    } else {
+        raw_s->fd = qemu_open(state->bs->filename, raw_s->open_flags, 0644);
+        if (raw_s->fd == -1) {
+            ret = -1;
+        }
+    }
+error:
+    return ret;
+}
+
+
+static void raw_reopen_commit(BDRVReopenState *state)
+{
+    BDRVRawReopenState *raw_s = state->opaque;
+    BDRVRawState *s = state->bs->opaque;
+
+    if (raw_s->aligned_buf != NULL) {
+        if (s->aligned_buf) {
+            qemu_vfree(s->aligned_buf);
+        }
+        s->aligned_buf      = raw_s->aligned_buf;
+        s->aligned_buf_size = raw_s->aligned_buf_size;
+    }
+
+    s->open_flags = raw_s->open_flags;
+
+    close(s->fd);
+    s->fd = raw_s->fd;
+
+    g_free(state->opaque);
+    state->opaque = NULL;
+}
+
+
+static void raw_reopen_abort(BDRVReopenState *state)
+{
+    BDRVRawReopenState *raw_s = state->opaque;
+
+     /* nothing to do if NULL, we didn't get far enough */
+    if (raw_s == NULL) {
+        return;
+    }
+
+    if (raw_s->fd >= 0) {
+        close(raw_s->fd);
+        raw_s->fd = -1;
+        if (raw_s->aligned_buf != NULL) {
+            qemu_vfree(raw_s->aligned_buf);
+        }
+    }
+    g_free(state->opaque);
+    state->opaque = NULL;
+}
+
+
 /* XXX: use host sector size if necessary with:
 #ifdef DIOCGSECTORSIZE
         {
@@ -735,6 +857,9 @@ static BlockDriver bdrv_file = {
     .instance_size = sizeof(BDRVRawState),
     .bdrv_probe = NULL, /* no probe for protocols */
     .bdrv_file_open = raw_open,
+    .bdrv_reopen_prepare = raw_reopen_prepare,
+    .bdrv_reopen_commit = raw_reopen_commit,
+    .bdrv_reopen_abort = raw_reopen_abort,
     .bdrv_close = raw_close,
     .bdrv_create = raw_create,
     .bdrv_co_discard = raw_co_discard,
-- 
1.7.11.2