Patchwork [11/12] migration: handle EAGAIN while reading QEMUFile

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Submitter Paolo Bonzini
Date Oct. 18, 2012, 10:22 a.m.
Message ID <1350555758-29988-12-git-send-email-pbonzini@redhat.com>
Download mbox | patch
Permalink /patch/192282/
State New
Headers show

Comments

Paolo Bonzini - Oct. 18, 2012, 10:22 a.m.
This will never happen right now (the assertion would fail).  The
next patch will set the socket or pipe in non-blocking mode, thus
enabling this part of the code.

Coroutines can just stop whenever they want with qemu_coroutine_yield.
As soon as select tells the main loop that the migration stream is
readable, the coroutine is re-entered directly in qemu_get_buffer,
where it will read more data and pass it to the loading routines.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 savevm.c | 30 ++++++++++++++++++++++++------
 1 file modificato, 24 inserzioni(+), 6 rimozioni(-)
Orit Wasserman - Oct. 28, 2012, 10:01 a.m.
On 10/18/2012 12:22 PM, Paolo Bonzini wrote:
> This will never happen right now (the assertion would fail).  The
> next patch will set the socket or pipe in non-blocking mode, thus
> enabling this part of the code.
> 
> Coroutines can just stop whenever they want with qemu_coroutine_yield.
> As soon as select tells the main loop that the migration stream is
> readable, the coroutine is re-entered directly in qemu_get_buffer,
> where it will read more data and pass it to the loading routines.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  savevm.c | 30 ++++++++++++++++++++++++------
>  1 file modificato, 24 inserzioni(+), 6 rimozioni(-)
> 
> diff --git a/savevm.c b/savevm.c
> index ae5e617..783bb3c 100644
> --- a/savevm.c
> +++ b/savevm.c
> @@ -199,13 +199,22 @@ static int socket_get_buffer(void *opaque, uint8_t *buf, int64_t pos, int size)
>      QEMUFileSocket *s = opaque;
>      ssize_t len;
>  
> -    do {
> +    for (;;) {
>          len = qemu_recv(s->fd, buf, size, 0);
> -    } while (len == -1 && socket_error() == EINTR);
> +        if (len != -1) {
> +            break;
> +        }
> +        if (errno == EAGAIN) {
socket_error()
> +            assert(qemu_in_coroutine());
> +            qemu_coroutine_yield();
> +        } else if (errno != EINTR) {
socket_error()
> +            break;
> +        }
> +    }
>  
> -    if (len == -1)
> +    if (len == -1) {
>          len = -socket_error();
> -
> +    }
>      return len;
>  }
>  
> @@ -236,10 +245,19 @@ static int stdio_get_buffer(void *opaque, uint8_t *buf, int64_t pos, int size)
>      FILE *fp = s->stdio_file;
>      int bytes;
>  
> -    do {
> +    for (;;) {
>          clearerr(fp);
>          bytes = fread(buf, 1, size, fp);
> -    } while ((bytes == 0) && ferror(fp) && (errno == EINTR));
> +        if (bytes != 0 || !ferror(fp)) {
> +            break;
> +        }
> +        if (errno == EAGAIN) {
> +            assert(qemu_in_coroutine());
> +            qemu_coroutine_yield();
> +        } else if (errno != EINTR) {
> +            break;
> +        }
> +    }
>      return bytes;
>  }
>  
>

Patch

diff --git a/savevm.c b/savevm.c
index ae5e617..783bb3c 100644
--- a/savevm.c
+++ b/savevm.c
@@ -199,13 +199,22 @@  static int socket_get_buffer(void *opaque, uint8_t *buf, int64_t pos, int size)
     QEMUFileSocket *s = opaque;
     ssize_t len;
 
-    do {
+    for (;;) {
         len = qemu_recv(s->fd, buf, size, 0);
-    } while (len == -1 && socket_error() == EINTR);
+        if (len != -1) {
+            break;
+        }
+        if (errno == EAGAIN) {
+            assert(qemu_in_coroutine());
+            qemu_coroutine_yield();
+        } else if (errno != EINTR) {
+            break;
+        }
+    }
 
-    if (len == -1)
+    if (len == -1) {
         len = -socket_error();
-
+    }
     return len;
 }
 
@@ -236,10 +245,19 @@  static int stdio_get_buffer(void *opaque, uint8_t *buf, int64_t pos, int size)
     FILE *fp = s->stdio_file;
     int bytes;
 
-    do {
+    for (;;) {
         clearerr(fp);
         bytes = fread(buf, 1, size, fp);
-    } while ((bytes == 0) && ferror(fp) && (errno == EINTR));
+        if (bytes != 0 || !ferror(fp)) {
+            break;
+        }
+        if (errno == EAGAIN) {
+            assert(qemu_in_coroutine());
+            qemu_coroutine_yield();
+        } else if (errno != EINTR) {
+            break;
+        }
+    }
     return bytes;
 }