Patchwork [3/4] migration: drop is_write complications

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Submitter Paolo Bonzini
Date April 8, 2013, 11:29 a.m.
Message ID <1365420597-5506-4-git-send-email-pbonzini@redhat.com>
Download mbox | patch
Permalink /patch/234742/
State New
Headers show

Comments

Paolo Bonzini - April 8, 2013, 11:29 a.m.
The same QEMUFile is never used for both read and write.  Simplify
the logic to simply look for presence or absence of the right ops.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 savevm.c | 68 +++++++++++++++++++---------------------------------------------
 1 file changed, 20 insertions(+), 48 deletions(-)
Juan Quintela - April 9, 2013, 11:42 a.m.
Paolo Bonzini <pbonzini@redhat.com> wrote:
> The same QEMUFile is never used for both read and write.  Simplify
> the logic to simply look for presence or absence of the right ops.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Love this one.

> @@ -556,11 +557,7 @@ static void qemu_fill_buffer(QEMUFile *f)
>      int len;
>      int pending;
>  
> -    if (!f->ops->get_buffer)
> -        return;

Why are we removing this test?  this has nothing to do with the is_write
removal?
And yes,  having a better way of knowing that the operations are there
looks like a good idea,  but that is independent of this series.


Thanks,  Juan.
Paolo Bonzini - April 9, 2013, 11:55 a.m.
Il 09/04/2013 13:42, Juan Quintela ha scritto:
>> > @@ -556,11 +557,7 @@ static void qemu_fill_buffer(QEMUFile *f)
>> >      int len;
>> >      int pending;
>> >  
>> > -    if (!f->ops->get_buffer)
>> > -        return;
> Why are we removing this test?  this has nothing to do with the is_write
> removal?

This test assumes that it makes sense to call qemu_get_byte on a
write-opened QEMUFile.  This is not true anymore after this patch.
After eliminating is_write, the right thing to do is abort.

Paolo

> And yes,  having a better way of knowing that the operations are there
> looks like a good idea,  but that is independent of this series.
Juan Quintela - April 9, 2013, 12:17 p.m.
Paolo Bonzini <pbonzini@redhat.com> wrote:
> Il 09/04/2013 13:42, Juan Quintela ha scritto:
>>> > @@ -556,11 +557,7 @@ static void qemu_fill_buffer(QEMUFile *f)
>>> >      int len;
>>> >      int pending;
>>> >  
>>> > -    if (!f->ops->get_buffer)
>>> > -        return;
>> Why are we removing this test?  this has nothing to do with the is_write
>> removal?
>
> This test assumes that it makes sense to call qemu_get_byte on a
> write-opened QEMUFile.  This is not true anymore after this patch.
> After eliminating is_write, the right thing to do is abort.


But this would not abort,  it would do a segmenation fault!

I would not complain to a:

assert(!f->ops->get_buffer);

It would told us from where we got the "invalid" call,  but this removal
will change a "silent fail" (that I don't like either) to a segmentation
fault (that is even worse).

Later,  Juan.
Paolo Bonzini - April 9, 2013, 12:25 p.m.
Il 09/04/2013 14:17, Juan Quintela ha scritto:
>> > This test assumes that it makes sense to call qemu_get_byte on a
>> > write-opened QEMUFile.  This is not true anymore after this patch.
>> > After eliminating is_write, the right thing to do is abort.
> 
> But this would not abort,  it would do a segmenation fault!
> 
> I would not complain to a:
> 
> assert(!f->ops->get_buffer);
> 
> It would told us from where we got the "invalid" call,  but this removal
> will change a "silent fail" (that I don't like either) to a segmentation
> fault (that is even worse).

It would still assert if you open a file in the wrong mode:

-    if (!f->ops->get_buffer)
-        return;
-
-    if (f->is_write)
-        abort();
+    assert(!qemu_file_is_writable(f));

It would segfault if you declare the QEMUFileOps wrong (e.g. no *_buffer
operation), but that's a bug in the QEMUFile implementation rather than
the usage.  I think a segfault is acceptable for that.

Paolo

Patch

diff --git a/savevm.c b/savevm.c
index b32e0a7..a2f6bc0 100644
--- a/savevm.c
+++ b/savevm.c
@@ -119,7 +119,6 @@  void qemu_announce_self(void)
 struct QEMUFile {
     const QEMUFileOps *ops;
     void *opaque;
-    int is_write;
 
     int64_t bytes_xfer;
     int64_t xfer_limit;
@@ -500,7 +499,6 @@  QEMUFile *qemu_fopen_ops(void *opaque, const QEMUFileOps *ops)
 
     f->opaque = opaque;
     f->ops = ops;
-    f->is_write = 0;
     return f;
 }
 
@@ -516,6 +514,11 @@  static void qemu_file_set_error(QEMUFile *f, int ret)
     }
 }
 
+static inline bool qemu_file_is_writable(QEMUFile *f)
+{
+    return f->ops->writev_buffer || f->ops->put_buffer;
+}
+
 /**
  * Flushes QEMUFile buffer
  *
@@ -526,26 +529,24 @@  static void qemu_fflush(QEMUFile *f)
 {
     ssize_t ret = 0;
 
-    if (!f->ops->writev_buffer && !f->ops->put_buffer) {
+    if (!qemu_file_is_writable(f)) {
         return;
     }
 
-    if (f->is_write) {
-        if (f->ops->writev_buffer) {
-            if (f->iovcnt > 0) {
-                ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt);
-            }
-        } else {
-            if (f->buf_index > 0) {
-                ret = f->ops->put_buffer(f->opaque, f->buf, f->pos, f->buf_index);
-            }
+    if (f->ops->writev_buffer) {
+        if (f->iovcnt > 0) {
+            ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt);
         }
-        if (ret >= 0) {
-            f->pos += ret;
+    } else {
+        if (f->buf_index > 0) {
+            ret = f->ops->put_buffer(f->opaque, f->buf, f->pos, f->buf_index);
         }
-        f->buf_index = 0;
-        f->iovcnt = 0;
     }
+    if (ret >= 0) {
+        f->pos += ret;
+    }
+    f->buf_index = 0;
+    f->iovcnt = 0;
     if (ret < 0) {
         qemu_file_set_error(f, ret);
     }
@@ -556,11 +557,7 @@  static void qemu_fill_buffer(QEMUFile *f)
     int len;
     int pending;
 
-    if (!f->ops->get_buffer)
-        return;
-
-    if (f->is_write)
-        abort();
+    assert(!qemu_file_is_writable(f));
 
     pending = f->buf_size - f->buf_index;
     if (pending > 0) {
@@ -629,7 +626,6 @@  static void add_to_iovec(QEMUFile *f, const uint8_t *buf, int size)
         f->iov[f->iovcnt++].iov_len = size;
     }
 
-    f->is_write = 1;
     if (f->buf_index >= IO_BUF_SIZE || f->iovcnt >= MAX_IOV_SIZE) {
         qemu_fflush(f);
     }
@@ -646,12 +642,6 @@  void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, int size)
         return;
     }
 
-    if (f->is_write == 0 && f->buf_index > 0) {
-        fprintf(stderr,
-                "Attempted to write to buffer while read buffer is not empty\n");
-        abort();
-    }
-
     f->bytes_xfer += size;
     add_to_iovec(f, buf, size);
 }
@@ -664,12 +654,6 @@  void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, int size)
         return;
     }
 
-    if (f->is_write == 0 && f->buf_index > 0) {
-        fprintf(stderr,
-                "Attempted to write to buffer while read buffer is not empty\n");
-        abort();
-    }
-
     while (size > 0) {
         l = IO_BUF_SIZE - f->buf_index;
         if (l > size)
@@ -680,7 +664,6 @@  void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, int size)
             add_to_iovec(f, f->buf + f->buf_index, l);
             f->buf_index += l;
         } else {
-            f->is_write = 1;
             f->buf_index += l;
             if (f->buf_index == IO_BUF_SIZE) {
                 qemu_fflush(f);
@@ -700,19 +683,12 @@  void qemu_put_byte(QEMUFile *f, int v)
         return;
     }
 
-    if (f->is_write == 0 && f->buf_index > 0) {
-        fprintf(stderr,
-                "Attempted to write to buffer while read buffer is not empty\n");
-        abort();
-    }
-
     f->buf[f->buf_index] = v;
     f->bytes_xfer++;
     if (f->ops->writev_buffer) {
         add_to_iovec(f, f->buf + f->buf_index, 1);
         f->buf_index++;
     } else {
-        f->is_write = 1;
         f->buf_index++;
         if (f->buf_index == IO_BUF_SIZE) {
             qemu_fflush(f);
@@ -732,9 +708,7 @@  static int qemu_peek_buffer(QEMUFile *f, uint8_t *buf, int size, size_t offset)
     int pending;
     int index;
 
-    if (f->is_write) {
-        abort();
-    }
+    assert(!qemu_file_is_writable(f));
 
     index = f->buf_index + offset;
     pending = f->buf_size - index;
@@ -779,9 +753,7 @@  static int qemu_peek_byte(QEMUFile *f, int offset)
 {
     int index = f->buf_index + offset;
 
-    if (f->is_write) {
-        abort();
-    }
+    assert(!qemu_file_is_writable(f));
 
     if (index >= f->buf_size) {
         qemu_fill_buffer(f);