Re: [PATCH 1/2] migration/compress: compress QEMUFile is not writable
"Dr. David Alan Gilbert" wrote:
> * Wei Yang (richardw.y...@linux.intel.com) wrote:
>> We open a file with empty_ops for compress QEMUFile, which means this is
>> not writable.
>
> That explanation sounds reasonable; but I'm confused by the history of
> this; the code was added by Liang Li in :
>
> b3be289 qemu-file: Fix qemu_put_compression_data flaw
>
> ( https://www.mail-archive.com/qemu-devel@nongnu.org/msg368974.html )
>
> with almost exactly the opposite argument; can we figure out why?
Comment of that patch is wrong, code agrees with this patch.
The patch that went in does:
-return 0;
+if (!qemu_file_is_writable(f)) {
+return -1;
+}
+qemu_fflush(f);
+blen = IO_BUF_SIZE - sizeof(int32_t);
+if (blen < compressBound(size)) {
+return -1;
+}
i.e. it move from return 0 to return -1 if we are not able to write, or
if we are not able to get enough space.
>> @@ -756,14 +753,7 @@ ssize_t qemu_put_compression_data(QEMUFile *f, z_stream
>> *stream,
>> ssize_t blen = IO_BUF_SIZE - f->buf_index - sizeof(int32_t);
>>
>> if (blen < compressBound(size)) {
>> -if (!qemu_file_is_writable(f)) {
>> -return -1;
>> -}
>> -qemu_fflush(f);
>> -blen = IO_BUF_SIZE - sizeof(int32_t);
>> -if (blen < compressBound(size)) {
>> -return -1;
>> -}
>> +return -1;
>> }
This moves from trying some things to just return -1.
And patch is ok. compression file has a file with empty_os, so
qemu_fflush() will not help at all.
Reviewed-by: Juan Quintela
Thanks, Juan.
Re: [PATCH 1/2] migration/compress: compress QEMUFile is not writable
On Thu, Nov 07, 2019 at 11:59:10AM +, Dr. David Alan Gilbert wrote: >* Wei Yang (richardw.y...@linux.intel.com) wrote: >> We open a file with empty_ops for compress QEMUFile, which means this is >> not writable. > >That explanation sounds reasonable; but I'm confused by the history of >this; the code was added by Liang Li in : > > b3be289 qemu-file: Fix qemu_put_compression_data flaw > > ( https://www.mail-archive.com/qemu-devel@nongnu.org/msg368974.html ) > >with almost exactly the opposite argument; can we figure out why? > Hmm... sounds interesting. Toke a look into the change log, which says Current qemu_put_compression_data can only work with no writable QEMUFile, and can't work with the writable QEMUFile. But it does not provide any measure to prevent users from using it with a writable QEMUFile. We should fix this flaw to make it works with writable QEMUFile. While I don't see a chance to use writable QEMUFile. Do I miss something? >Dave > -- Wei Yang Help you, Help me
Re: [PATCH 1/2] migration/compress: compress QEMUFile is not writable
* Wei Yang (richardw.y...@linux.intel.com) wrote:
> We open a file with empty_ops for compress QEMUFile, which means this is
> not writable.
That explanation sounds reasonable; but I'm confused by the history of
this; the code was added by Liang Li in :
b3be289 qemu-file: Fix qemu_put_compression_data flaw
( https://www.mail-archive.com/qemu-devel@nongnu.org/msg368974.html )
with almost exactly the opposite argument; can we figure out why?
Dave
> Signed-off-by: Wei Yang
> ---
> migration/qemu-file.c | 16 +++-
> 1 file changed, 3 insertions(+), 13 deletions(-)
>
> diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> index 26fb25ddc1..f3d99a96ec 100644
> --- a/migration/qemu-file.c
> +++ b/migration/qemu-file.c
> @@ -744,11 +744,8 @@ static int qemu_compress_data(z_stream *stream, uint8_t
> *dest, size_t dest_len,
> /* Compress size bytes of data start at p and store the compressed
> * data to the buffer of f.
> *
> - * When f is not writable, return -1 if f has no space to save the
> - * compressed data.
> - * When f is wirtable and it has no space to save the compressed data,
> - * do fflush first, if f still has no space to save the compressed
> - * data, return -1.
> + * Since the file is dummy file with empty_ops, return -1 if f has no space
> to
> + * save the compressed data.
> */
> ssize_t qemu_put_compression_data(QEMUFile *f, z_stream *stream,
>const uint8_t *p, size_t size)
> @@ -756,14 +753,7 @@ ssize_t qemu_put_compression_data(QEMUFile *f, z_stream
> *stream,
> ssize_t blen = IO_BUF_SIZE - f->buf_index - sizeof(int32_t);
>
> if (blen < compressBound(size)) {
> -if (!qemu_file_is_writable(f)) {
> -return -1;
> -}
> -qemu_fflush(f);
> -blen = IO_BUF_SIZE - sizeof(int32_t);
> -if (blen < compressBound(size)) {
> -return -1;
> -}
> +return -1;
> }
>
> blen = qemu_compress_data(stream, f->buf + f->buf_index +
> sizeof(int32_t),
> --
> 2.17.1
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
[PATCH 1/2] migration/compress: compress QEMUFile is not writable
We open a file with empty_ops for compress QEMUFile, which means this is
not writable.
Signed-off-by: Wei Yang
---
migration/qemu-file.c | 16 +++-
1 file changed, 3 insertions(+), 13 deletions(-)
diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index 26fb25ddc1..f3d99a96ec 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -744,11 +744,8 @@ static int qemu_compress_data(z_stream *stream, uint8_t
*dest, size_t dest_len,
/* Compress size bytes of data start at p and store the compressed
* data to the buffer of f.
*
- * When f is not writable, return -1 if f has no space to save the
- * compressed data.
- * When f is wirtable and it has no space to save the compressed data,
- * do fflush first, if f still has no space to save the compressed
- * data, return -1.
+ * Since the file is dummy file with empty_ops, return -1 if f has no space to
+ * save the compressed data.
*/
ssize_t qemu_put_compression_data(QEMUFile *f, z_stream *stream,
const uint8_t *p, size_t size)
@@ -756,14 +753,7 @@ ssize_t qemu_put_compression_data(QEMUFile *f, z_stream
*stream,
ssize_t blen = IO_BUF_SIZE - f->buf_index - sizeof(int32_t);
if (blen < compressBound(size)) {
-if (!qemu_file_is_writable(f)) {
-return -1;
-}
-qemu_fflush(f);
-blen = IO_BUF_SIZE - sizeof(int32_t);
-if (blen < compressBound(size)) {
-return -1;
-}
+return -1;
}
blen = qemu_compress_data(stream, f->buf + f->buf_index + sizeof(int32_t),
--
2.17.1
