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Re: [PATCH v5 06/14] migration/qemu-file: Add qemu_file_get_to_fd()


From: Avihai Horon
Subject: Re: [PATCH v5 06/14] migration/qemu-file: Add qemu_file_get_to_fd()
Date: Mon, 9 Jan 2023 17:18:58 +0200
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.6.1


On 09/01/2023 13:20, Cédric Le Goater wrote:
External email: Use caution opening links or attachments


On 12/29/22 12:03, Avihai Horon wrote:
Add new function qemu_file_get_to_fd() that allows reading data from
QEMUFile and writing it straight into a given fd.

This will be used later in VFIO migration code.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
  migration/qemu-file.h |  1 +
  migration/qemu-file.c | 34 ++++++++++++++++++++++++++++++++++
  2 files changed, 35 insertions(+)

diff --git a/migration/qemu-file.h b/migration/qemu-file.h
index fa13d04d78..9d0155a2a1 100644
--- a/migration/qemu-file.h
+++ b/migration/qemu-file.h
@@ -148,6 +148,7 @@ int qemu_file_shutdown(QEMUFile *f);
  QEMUFile *qemu_file_get_return_path(QEMUFile *f);
  void qemu_fflush(QEMUFile *f);
  void qemu_file_set_blocking(QEMUFile *f, bool block);
+int qemu_file_get_to_fd(QEMUFile *f, int fd, size_t size);

  void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
  void ram_control_after_iterate(QEMUFile *f, uint64_t flags);
diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index 2d5f74ffc2..79303c9d34 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -940,3 +940,37 @@ QIOChannel *qemu_file_get_ioc(QEMUFile *file)
  {
      return file->ioc;
  }
+
+/*
+ * Read size bytes from QEMUFile f and write them to fd.
+ */
+int qemu_file_get_to_fd(QEMUFile *f, int fd, size_t size)
+{
+    while (size) {
+        size_t pending = f->buf_size - f->buf_index;
+        ssize_t rc;
+
+        if (!pending) {
+            rc = qemu_fill_buffer(f);
+            if (rc < 0) {
+                return rc;
+            }
+            if (rc == 0) {
+                return -1;

Given the call stack, -1 would be interpreted  as EPERM. May be EIO instead ?

Sure.

I will also change write (down below) to return -errno instead of rc on error.

C.

+            }
+            continue;
+        }
+
+        rc = write(fd, f->buf + f->buf_index, MIN(pending, size));
+        if (rc < 0) {
+            return rc;
+        }
+        if (rc == 0) {
+            return -1;
+        }
+        f->buf_index += rc;
+        size -= rc;
+    }
+
+    return 0;
+}




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