Make 'qemu-img commit' work on Windows.

Command 'commit' requires reopening backing file in RW mode. So,
add reopen prepare/commit/abort handlers and change dwShareMode
for CreateFile call in order to allow further read/write reopening.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/418
Suggested-by: Hanna Reitz <hreitz@redhat.com>
Signed-off-by: Viktor Prutyanov <viktor.prutyanov@phystech.edu>
---
 block/file-win32.c | 85 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 84 insertions(+), 1 deletion(-)

diff --git a/block/file-win32.c b/block/file-win32.c
index 2642088bd6..e44878e6be 100644
--- a/block/file-win32.c
+++ b/block/file-win32.c
@@ -58,6 +58,10 @@ typedef struct BDRVRawState {
     QEMUWin32AIOState *aio;
 } BDRVRawState;
 
+typedef struct BDRVRawReopenState {
+    HANDLE hfile;
+} BDRVRawReopenState;
+
 /*
  * Read/writes the data to/from a given linear buffer.
  *
@@ -392,7 +396,7 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     s->hfile = CreateFile(filename, access_flags,
-                          FILE_SHARE_READ, NULL,
+                          FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
                           OPEN_EXISTING, overlapped, NULL);
     if (s->hfile == INVALID_HANDLE_VALUE) {
         int err = GetLastError();
@@ -634,6 +638,81 @@ static int coroutine_fn raw_co_create_opts(BlockDriver *drv,
     return raw_co_create(&options, errp);
 }
 
+static int raw_reopen_prepare(BDRVReopenState *state,
+        BlockReopenQueue *queue, Error **errp)
+{
+    BDRVRawState *s = state->bs->opaque;
+    BDRVRawReopenState *rs;
+    int access_flags;
+    DWORD overlapped;
+    int ret = 0;
+
+    rs = state->opaque = g_new0(BDRVRawReopenState, 1);
+
+    raw_parse_flags(state->flags, s->aio != NULL, &access_flags, &overlapped);
+    rs->hfile = CreateFile(state->bs->filename, access_flags,
+                           FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
+                           OPEN_EXISTING, overlapped, NULL);
+
+    if (rs->hfile == INVALID_HANDLE_VALUE) {
+        int err = GetLastError();
+
+        error_setg_win32(errp, err, "Could not reopen '%s'",
+                         state->bs->filename);
+        if (err == ERROR_ACCESS_DENIED) {
+            ret = -EACCES;
+        } else {
+            ret = -EINVAL;
+        }
+        goto fail;
+    }
+
+    if (s->aio) {
+        ret = win32_aio_attach(s->aio, rs->hfile);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Could not enable AIO");
+            goto fail;
+        }
+    }
+
+    return 0;
+
+fail:
+    return ret;
+}
+
+static void raw_reopen_commit(BDRVReopenState *state)
+{
+    BDRVRawState *s = state->bs->opaque;
+    BDRVRawReopenState *rs = state->opaque;
+
+    if (!rs) {
+        return;
+    }
+
+    CloseHandle(s->hfile);
+    s->hfile = rs->hfile;
+
+    g_free(rs);
+    state->opaque = NULL;
+}
+
+static void raw_reopen_abort(BDRVReopenState *state)
+{
+    BDRVRawReopenState *rs = state->opaque;
+
+    if (!rs) {
+        return;
+    }
+
+    if (rs->hfile != INVALID_HANDLE_VALUE) {
+        CloseHandle(rs->hfile);
+    }
+
+    g_free(rs);
+    state->opaque = NULL;
+}
+
 static QemuOptsList raw_create_opts = {
     .name = "raw-create-opts",
     .head = QTAILQ_HEAD_INITIALIZER(raw_create_opts.head),
@@ -659,6 +738,10 @@ BlockDriver bdrv_file = {
     .bdrv_co_create_opts = raw_co_create_opts,
     .bdrv_has_zero_init = bdrv_has_zero_init_1,
 
+    .bdrv_reopen_prepare = raw_reopen_prepare,
+    .bdrv_reopen_commit  = raw_reopen_commit,
+    .bdrv_reopen_abort   = raw_reopen_abort,
+
     .bdrv_aio_preadv    = raw_aio_preadv,
     .bdrv_aio_pwritev   = raw_aio_pwritev,
     .bdrv_aio_flush     = raw_aio_flush,
-- 
2.21.0

Hi Viktor,

Thanks for the patch :)

On 8/17/21 12:12 PM, Viktor Prutyanov wrote:
> Make 'qemu-img commit' work on Windows.
> 
> Command 'commit' requires reopening backing file in RW mode. So,
> add reopen prepare/commit/abort handlers and change dwShareMode
> for CreateFile call in order to allow further read/write reopening.
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/418
> Suggested-by: Hanna Reitz <hreitz@redhat.com>
> Signed-off-by: Viktor Prutyanov <viktor.prutyanov@phystech.edu>
> ---
>  block/file-win32.c | 85 +++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 84 insertions(+), 1 deletion(-)
> 
> diff --git a/block/file-win32.c b/block/file-win32.c
> index 2642088bd6..e44878e6be 100644
> --- a/block/file-win32.c
> +++ b/block/file-win32.c
> @@ -58,6 +58,10 @@ typedef struct BDRVRawState {
>      QEMUWin32AIOState *aio;
>  } BDRVRawState;
>  
> +typedef struct BDRVRawReopenState {
> +    HANDLE hfile;
> +} BDRVRawReopenState;
> +
>  /*
>   * Read/writes the data to/from a given linear buffer.
>   *
> @@ -392,7 +396,7 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags,
>      }
>  
>      s->hfile = CreateFile(filename, access_flags,
> -                          FILE_SHARE_READ, NULL,
> +                          FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
>                            OPEN_EXISTING, overlapped, NULL);
>      if (s->hfile == INVALID_HANDLE_VALUE) {
>          int err = GetLastError();
> @@ -634,6 +638,81 @@ static int coroutine_fn raw_co_create_opts(BlockDriver *drv,
>      return raw_co_create(&options, errp);
>  }
>  
> +static int raw_reopen_prepare(BDRVReopenState *state,
> +        BlockReopenQueue *queue, Error **errp)

Invalid style alignment.

> +{
> +    BDRVRawState *s = state->bs->opaque;
> +    BDRVRawReopenState *rs;
> +    int access_flags;
> +    DWORD overlapped;
> +    int ret = 0;
> +
> +    rs = state->opaque = g_new0(BDRVRawReopenState, 1);
> +
> +    raw_parse_flags(state->flags, s->aio != NULL, &access_flags, &overlapped);
> +    rs->hfile = CreateFile(state->bs->filename, access_flags,
> +                           FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
> +                           OPEN_EXISTING, overlapped, NULL);
> +
> +    if (rs->hfile == INVALID_HANDLE_VALUE) {
> +        int err = GetLastError();
> +
> +        error_setg_win32(errp, err, "Could not reopen '%s'",
> +                         state->bs->filename);
> +        if (err == ERROR_ACCESS_DENIED) {
> +            ret = -EACCES;
> +        } else {
> +            ret = -EINVAL;
> +        }
> +        goto fail;
> +    }
> +
> +    if (s->aio) {
> +        ret = win32_aio_attach(s->aio, rs->hfile);
> +        if (ret < 0) {
> +            error_setg_errno(errp, -ret, "Could not enable AIO");
> +            goto fail;
> +        }
> +    }
To avoid non-NULL value in state->opaque on failure,
I'd use in prologue:

       rs = g_new0(BDRVRawReopenState, 1);

and here:

       state->opaque = rs;

> +    return 0;
> +
> +fail:

Shouldn't we free state->opaque on failure? (I'm not sure because
I don't know well the bdrv_reopen_prepare handler).

> +    return ret;
> +}
> +
> +static void raw_reopen_commit(BDRVReopenState *state)
> +{
> +    BDRVRawState *s = state->bs->opaque;
> +    BDRVRawReopenState *rs = state->opaque;
> +
> +    if (!rs) {

Indeed, raw_reopen_prepare() could let state->opaque non-NULL.

> +        return;
> +    }
> +
> +    CloseHandle(s->hfile);
> +    s->hfile = rs->hfile;
> +
> +    g_free(rs);
> +    state->opaque = NULL;
> +}
> +
> +static void raw_reopen_abort(BDRVReopenState *state)
> +{
> +    BDRVRawReopenState *rs = state->opaque;
> +
> +    if (!rs) {
> +        return;
> +    }
> +
> +    if (rs->hfile != INVALID_HANDLE_VALUE) {
> +        CloseHandle(rs->hfile);
> +    }
> +
> +    g_free(rs);
> +    state->opaque = NULL;
> +}
> +
>  static QemuOptsList raw_create_opts = {
>      .name = "raw-create-opts",
>      .head = QTAILQ_HEAD_INITIALIZER(raw_create_opts.head),
> @@ -659,6 +738,10 @@ BlockDriver bdrv_file = {
>      .bdrv_co_create_opts = raw_co_create_opts,
>      .bdrv_has_zero_init = bdrv_has_zero_init_1,
>  
> +    .bdrv_reopen_prepare = raw_reopen_prepare,
> +    .bdrv_reopen_commit  = raw_reopen_commit,
> +    .bdrv_reopen_abort   = raw_reopen_abort,
> +
>      .bdrv_aio_preadv    = raw_aio_preadv,
>      .bdrv_aio_pwritev   = raw_aio_pwritev,
>      .bdrv_aio_flush     = raw_aio_flush,
>