io/channel: introduce qio_channel_pread{v, }_all{, _eof}()

qio_channel_pread() and qio_channel_preadv() perform a single
positioned read and may return a short result.  Callers that need all
bytes currently have to open-code a retry loop or simply treat a short
read as an error.

Introduce four new helpers following the existing read_all / readv_all
pattern:

  qio_channel_preadv_all_eof()  -- retry loop; returns 1 on success,
                                    0 on clean EOF, -1 on error.
  qio_channel_preadv_all()      -- wraps _eof; treats early EOF as
                                    error; returns 0 / -1.
  qio_channel_pread_all_eof()   -- single-buffer convenience wrapper
                                    around preadv_all_eof().
  qio_channel_pread_all()       -- single-buffer convenience wrapper
                                    around preadv_all().

These advance the file offset internally after each partial read.
All four are marked coroutine_mixed_fn, consistent with the existing
_all helpers.

Suggested-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Junjie Cao <junjie.cao@intel.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Acked-by: Daniel P. Berrangé <berrange@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20260413214549.926435-2-junjie.cao@intel.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>

diff --git a/include/io/channel.h b/include/io/channel.h
index 1b02350437d5b0582ae2c4e79f8bd1d63b964b4a..47af409ede8e5f2b6b7f877a81c0664a2bddf5eb 100644 (file)
--- a/include/io/channel.h
+++ b/include/io/channel.h
@@ -634,6 +634,98 @@ ssize_t qio_channel_preadv(QIOChannel *ioc, const struct iovec *iov,
 ssize_t qio_channel_pread(QIOChannel *ioc, void *buf, size_t buflen,
                           off_t offset, Error **errp);
 
+/**
+ * qio_channel_preadv_all_eof:
+ * @ioc: the channel object
+ * @iov: the array of memory regions to read data into
+ * @niov: the length of the @iov array
+ * @offset: the starting offset in the channel to read from
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Reads @iov, possibly blocking or (if the channel is non-blocking)
+ * yielding from the current coroutine multiple times until the entire
+ * content is read.  If end-of-file occurs immediately it is not an
+ * error, but if it occurs after data has been read it will return
+ * an error rather than a short-read.  Otherwise behaves as
+ * qio_channel_preadv().
+ *
+ * Returns: 1 if all bytes were read, 0 if end-of-file occurs
+ *          without data, or -1 on error
+ */
+int coroutine_mixed_fn qio_channel_preadv_all_eof(QIOChannel *ioc,
+                                                  const struct iovec *iov,
+                                                  size_t niov,
+                                                  off_t offset,
+                                                  Error **errp);
+
+/**
+ * qio_channel_preadv_all:
+ * @ioc: the channel object
+ * @iov: the array of memory regions to read data into
+ * @niov: the length of the @iov array
+ * @offset: the starting offset in the channel to read from
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Reads @iov, possibly blocking or (if the channel is non-blocking)
+ * yielding from the current coroutine multiple times until the entire
+ * content is read.  If end-of-file occurs before all requested data
+ * has been read, an error will be reported.  Otherwise behaves as
+ * qio_channel_preadv().
+ *
+ * Returns: 0 if all bytes were read, or -1 on error
+ */
+int coroutine_mixed_fn qio_channel_preadv_all(QIOChannel *ioc,
+                                              const struct iovec *iov,
+                                              size_t niov,
+                                              off_t offset,
+                                              Error **errp);
+
+/**
+ * qio_channel_pread_all_eof:
+ * @ioc: the channel object
+ * @buf: the memory region to read data into
+ * @buflen: the number of bytes to read into @buf
+ * @offset: the starting offset in the channel to read from
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Reads @buflen bytes, possibly blocking or (if the channel is
+ * non-blocking) yielding from the current coroutine multiple times
+ * until the entire content is read.  If end-of-file occurs
+ * immediately it is not an error, but if it occurs after data has
+ * been read it will return an error rather than a short-read.
+ * Otherwise behaves as qio_channel_pread().
+ *
+ * Returns: 1 if all bytes were read, 0 if end-of-file occurs
+ *          without data, or -1 on error
+ */
+int coroutine_mixed_fn qio_channel_pread_all_eof(QIOChannel *ioc,
+                                                 void *buf,
+                                                 size_t buflen,
+                                                 off_t offset,
+                                                 Error **errp);
+
+/**
+ * qio_channel_pread_all:
+ * @ioc: the channel object
+ * @buf: the memory region to read data into
+ * @buflen: the number of bytes to read into @buf
+ * @offset: the starting offset in the channel to read from
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Reads @buflen bytes, possibly blocking or (if the channel is
+ * non-blocking) yielding from the current coroutine multiple times
+ * until the entire content is read.  If end-of-file occurs before
+ * all requested data has been read, an error will be reported.
+ * Otherwise behaves as qio_channel_pread().
+ *
+ * Returns: 0 if all bytes were read, or -1 on error
+ */
+int coroutine_mixed_fn qio_channel_pread_all(QIOChannel *ioc,
+                                             void *buf,
+                                             size_t buflen,
+                                             off_t offset,
+                                             Error **errp);
+
 /**
  * qio_channel_shutdown:
  * @ioc: the channel object

diff --git a/io/channel.c b/io/channel.c
index cc02d997a4dae475759b228f41c29e51d73fb676..52c1abfcbca6db524dc18592500bb1b9bd2358f7 100644 (file)
--- a/io/channel.c
+++ b/io/channel.c
@@ -507,6 +507,97 @@ ssize_t qio_channel_pread(QIOChannel *ioc, void *buf, size_t buflen,
     return qio_channel_preadv(ioc, &iov, 1, offset, errp);
 }
 
+int coroutine_mixed_fn qio_channel_preadv_all_eof(QIOChannel *ioc,
+                                                  const struct iovec *iov,
+                                                  size_t niov,
+                                                  off_t offset,
+                                                  Error **errp)
+{
+    int ret = -1;
+    struct iovec *local_iov = g_new(struct iovec, niov);
+    struct iovec *local_iov_head = local_iov;
+    unsigned int nlocal_iov = niov;
+    bool partial = false;
+
+    nlocal_iov = iov_copy(local_iov, nlocal_iov,
+                          iov, niov,
+                          0, iov_size(iov, niov));
+
+    while (nlocal_iov > 0) {
+        ssize_t len;
+        len = qio_channel_preadv(ioc, local_iov, nlocal_iov, offset, errp);
+
+        if (len == QIO_CHANNEL_ERR_BLOCK) {
+            qio_channel_wait_cond(ioc, G_IO_IN);
+            continue;
+        }
+
+        if (len == 0) {
+            if (!partial) {
+                ret = 0;
+                goto cleanup;
+            }
+            error_setg(errp,
+                       "Unexpected end-of-file before all data were read");
+            goto cleanup;
+        }
+
+        if (len < 0) {
+            goto cleanup;
+        }
+
+        partial = true;
+        offset += len;
+        iov_discard_front(&local_iov, &nlocal_iov, len);
+    }
+
+    ret = 1;
+
+ cleanup:
+    g_free(local_iov_head);
+    return ret;
+}
+
+int coroutine_mixed_fn qio_channel_preadv_all(QIOChannel *ioc,
+                                              const struct iovec *iov,
+                                              size_t niov,
+                                              off_t offset,
+                                              Error **errp)
+{
+    int ret = qio_channel_preadv_all_eof(ioc, iov, niov, offset, errp);
+
+    if (ret == 0) {
+        error_setg(errp,
+                   "Unexpected end-of-file before all data were read");
+        return -1;
+    }
+    if (ret == 1) {
+        return 0;
+    }
+
+    return ret;
+}
+
+int coroutine_mixed_fn qio_channel_pread_all_eof(QIOChannel *ioc,
+                                                 void *buf,
+                                                 size_t buflen,
+                                                 off_t offset,
+                                                 Error **errp)
+{
+    struct iovec iov = { .iov_base = buf, .iov_len = buflen };
+    return qio_channel_preadv_all_eof(ioc, &iov, 1, offset, errp);
+}
+
+int coroutine_mixed_fn qio_channel_pread_all(QIOChannel *ioc,
+                                             void *buf,
+                                             size_t buflen,
+                                             off_t offset,
+                                             Error **errp)
+{
+    struct iovec iov = { .iov_base = buf, .iov_len = buflen };
+    return qio_channel_preadv_all(ioc, &iov, 1, offset, errp);
+}
+
 int qio_channel_shutdown(QIOChannel *ioc,
                          QIOChannelShutdown how,
                          Error **errp)