migration/qemu-file-buf.c - qemu - Git at Google

 /*
  * QEMU System Emulator
  *
  * Copyright (c) 2003-2008 Fabrice Bellard
  * Copyright (c) 2014 IBM Corp.
  *
  * Authors:
  *  Stefan Berger <stefanb@linux.vnet.ibm.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
 #include "qemu-common.h"
 #include "qemu/error-report.h"
 #include "qemu/iov.h"
 #include "qemu/sockets.h"
 #include "qemu/coroutine.h"
 #include "migration/migration.h"
 #include "migration/qemu-file.h"
 #include "migration/qemu-file-internal.h"
 #include "trace.h"

 #define QSB_CHUNK_SIZE      (1 << 10)
 #define QSB_MAX_CHUNK_SIZE  (16 * QSB_CHUNK_SIZE)

 /**
  * Create a QEMUSizedBuffer
  * This type of buffer uses scatter-gather lists internally and
  * can grow to any size. Any data array in the scatter-gather list
  * can hold different amount of bytes.
  *
  * @buffer: Optional buffer to copy into the QSB
  * @len: size of initial buffer; if @buffer is given, buffer must
  *       hold at least len bytes
  *
  * Returns a pointer to a QEMUSizedBuffer or NULL on allocation failure
  */
 QEMUSizedBuffer *qsb_create(const uint8_t *buffer, size_t len)
 {
     QEMUSizedBuffer *qsb;
     size_t alloc_len, num_chunks, i, to_copy;
     size_t chunk_size = (len > QSB_MAX_CHUNK_SIZE)
                         ? QSB_MAX_CHUNK_SIZE
                         : QSB_CHUNK_SIZE;

     num_chunks = DIV_ROUND_UP(len ? len : QSB_CHUNK_SIZE, chunk_size);
     alloc_len = num_chunks * chunk_size;

     qsb = g_try_new0(QEMUSizedBuffer, 1);
     if (!qsb) {
         return NULL;
     }

     qsb->iov = g_try_new0(struct iovec, num_chunks);
     if (!qsb->iov) {
         g_free(qsb);
         return NULL;
     }

     qsb->n_iov = num_chunks;

     for (i = 0; i < num_chunks; i++) {
         qsb->iov[i].iov_base = g_try_malloc0(chunk_size);
         if (!qsb->iov[i].iov_base) {
             /* qsb_free is safe since g_free can cope with NULL */
             qsb_free(qsb);
             return NULL;
         }

         qsb->iov[i].iov_len = chunk_size;
         if (buffer) {
             to_copy = (len - qsb->used) > chunk_size
                       ? chunk_size : (len - qsb->used);
             memcpy(qsb->iov[i].iov_base, &buffer[qsb->used], to_copy);
             qsb->used += to_copy;
         }
     }

     qsb->size = alloc_len;

     return qsb;
 }

 /**
  * Free the QEMUSizedBuffer
  *
  * @qsb: The QEMUSizedBuffer to free
  */
 void qsb_free(QEMUSizedBuffer *qsb)
 {
     size_t i;

     if (!qsb) {
         return;
     }

     for (i = 0; i < qsb->n_iov; i++) {
         g_free(qsb->iov[i].iov_base);
     }
     g_free(qsb->iov);
     g_free(qsb);
 }

 /**
  * Get the number of used bytes in the QEMUSizedBuffer
  *
  * @qsb: A QEMUSizedBuffer
  *
  * Returns the number of bytes currently used in this buffer
  */
 size_t qsb_get_length(const QEMUSizedBuffer *qsb)
 {
     return qsb->used;
 }

 /**
  * Set the length of the buffer; the primary usage of this
  * function is to truncate the number of used bytes in the buffer.
  * The size will not be extended beyond the current number of
  * allocated bytes in the QEMUSizedBuffer.
  *
  * @qsb: A QEMUSizedBuffer
  * @new_len: The new length of bytes in the buffer
  *
  * Returns the number of bytes the buffer was truncated or extended
  * to.
  */
 size_t qsb_set_length(QEMUSizedBuffer *qsb, size_t new_len)
 {
     if (new_len <= qsb->size) {
         qsb->used = new_len;
     } else {
         qsb->used = qsb->size;
     }
     return qsb->used;
 }

 /**
  * Get the iovec that holds the data for a given position @pos.
  *
  * @qsb: A QEMUSizedBuffer
  * @pos: The index of a byte in the buffer
  * @d_off: Pointer to an offset that this function will indicate
  *         at what position within the returned iovec the byte
  *         is to be found
  *
  * Returns the index of the iovec that holds the byte at the given
  * index @pos in the byte stream; a negative number if the iovec
  * for the given position @pos does not exist.
  */
 static ssize_t qsb_get_iovec(const QEMUSizedBuffer *qsb,
                              off_t pos, off_t *d_off)
 {
     ssize_t i;
     off_t curr = 0;

     if (pos > qsb->used) {
         return -1;
     }

     for (i = 0; i < qsb->n_iov; i++) {
         if (curr + qsb->iov[i].iov_len > pos) {
             *d_off = pos - curr;
             return i;
         }
         curr += qsb->iov[i].iov_len;
     }
     return -1;
 }

 /*
  * Convert the QEMUSizedBuffer into a flat buffer.
  *
  * Note: If at all possible, try to avoid this function since it
  *       may unnecessarily copy memory around.
  *
  * @qsb: pointer to QEMUSizedBuffer
  * @start: offset to start at
  * @count: number of bytes to copy
  * @buf: a pointer to a buffer to write into (at least @count bytes)
  *
  * Returns the number of bytes copied into the output buffer
  */
 ssize_t qsb_get_buffer(const QEMUSizedBuffer *qsb, off_t start,
                        size_t count, uint8_t *buffer)
 {
     const struct iovec *iov;
     size_t to_copy, all_copy;
     ssize_t index;
     off_t s_off;
     off_t d_off = 0;
     char *s;

     if (start > qsb->used) {
         return 0;
     }

     all_copy = qsb->used - start;
     if (all_copy > count) {
         all_copy = count;
     } else {
         count = all_copy;
     }

     index = qsb_get_iovec(qsb, start, &s_off);
     if (index < 0) {
         return 0;
     }

     while (all_copy > 0) {
         iov = &qsb->iov[index];

         s = iov->iov_base;

         to_copy = iov->iov_len - s_off;
         if (to_copy > all_copy) {
             to_copy = all_copy;
         }
         memcpy(&buffer[d_off], &s[s_off], to_copy);

         d_off += to_copy;
         all_copy -= to_copy;

         s_off = 0;
         index++;
     }

     return count;
 }

 /**
  * Grow the QEMUSizedBuffer to the given size and allocate
  * memory for it.
  *
  * @qsb: A QEMUSizedBuffer
  * @new_size: The new size of the buffer
  *
  * Return:
  *    a negative error code in case of memory allocation failure
  * or
  *    the new size of the buffer. The returned size may be greater or equal
  *    to @new_size.
  */
 static ssize_t qsb_grow(QEMUSizedBuffer *qsb, size_t new_size)
 {
     size_t needed_chunks, i;

     if (qsb->size < new_size) {
         struct iovec *new_iov;
         size_t size_diff = new_size - qsb->size;
         size_t chunk_size = (size_diff > QSB_MAX_CHUNK_SIZE)
                              ? QSB_MAX_CHUNK_SIZE : QSB_CHUNK_SIZE;

         needed_chunks = DIV_ROUND_UP(size_diff, chunk_size);

         new_iov = g_try_new(struct iovec, qsb->n_iov + needed_chunks);
         if (new_iov == NULL) {
             return -ENOMEM;
         }

         /* Allocate new chunks as needed into new_iov */
         for (i = qsb->n_iov; i < qsb->n_iov + needed_chunks; i++) {
             new_iov[i].iov_base = g_try_malloc0(chunk_size);
             new_iov[i].iov_len = chunk_size;
             if (!new_iov[i].iov_base) {
                 size_t j;

                 /* Free previously allocated new chunks */
                 for (j = qsb->n_iov; j < i; j++) {
                     g_free(new_iov[j].iov_base);
                 }
                 g_free(new_iov);

                 return -ENOMEM;
             }
         }

         /*
          * Now we can't get any allocation errors, copy over to new iov
          * and switch.
          */
         for (i = 0; i < qsb->n_iov; i++) {
             new_iov[i] = qsb->iov[i];
         }

         qsb->n_iov += needed_chunks;
         g_free(qsb->iov);
         qsb->iov = new_iov;
         qsb->size += (needed_chunks * chunk_size);
     }

     return qsb->size;
 }

 /**
  * Write into the QEMUSizedBuffer at a given position and a given
  * number of bytes. This function will automatically grow the
  * QEMUSizedBuffer.
  *
  * @qsb: A QEMUSizedBuffer
  * @source: A byte array to copy data from
  * @pos: The position within the @qsb to write data to
  * @size: The number of bytes to copy into the @qsb
  *
  * Returns @size or a negative error code in case of memory allocation failure,
  *           or with an invalid 'pos'
  */
 ssize_t qsb_write_at(QEMUSizedBuffer *qsb, const uint8_t *source,
                      off_t pos, size_t count)
 {
     ssize_t rc = qsb_grow(qsb, pos + count);
     size_t to_copy;
     size_t all_copy = count;
     const struct iovec *iov;
     ssize_t index;
     char *dest;
     off_t d_off, s_off = 0;

     if (rc < 0) {
         return rc;
     }

     if (pos + count > qsb->used) {
         qsb->used = pos + count;
     }

     index = qsb_get_iovec(qsb, pos, &d_off);
     if (index < 0) {
         return -EINVAL;
     }

     while (all_copy > 0) {
         iov = &qsb->iov[index];

         dest = iov->iov_base;

         to_copy = iov->iov_len - d_off;
         if (to_copy > all_copy) {
             to_copy = all_copy;
         }

         memcpy(&dest[d_off], &source[s_off], to_copy);

         s_off += to_copy;
         all_copy -= to_copy;

         d_off = 0;
         index++;
     }

     return count;
 }

 typedef struct QEMUBuffer {
     QEMUSizedBuffer *qsb;
     QEMUFile *file;
     bool qsb_allocated;
 } QEMUBuffer;

 static ssize_t buf_get_buffer(void *opaque, uint8_t *buf, int64_t pos,
                               size_t size)
 {
     QEMUBuffer *s = opaque;
     ssize_t len = qsb_get_length(s->qsb) - pos;

     if (len <= 0) {
         return 0;
     }

     if (len > size) {
         len = size;
     }
     return qsb_get_buffer(s->qsb, pos, len, buf);
 }

 static ssize_t buf_put_buffer(void *opaque, const uint8_t *buf,
                               int64_t pos, size_t size)
 {
     QEMUBuffer *s = opaque;

     return qsb_write_at(s->qsb, buf, pos, size);
 }

 static int buf_close(void *opaque)
 {
     QEMUBuffer *s = opaque;

     if (s->qsb_allocated) {
         qsb_free(s->qsb);
     }

     g_free(s);

     return 0;
 }

 const QEMUSizedBuffer *qemu_buf_get(QEMUFile *f)
 {
     QEMUBuffer *p;

     qemu_fflush(f);

     p = f->opaque;

     return p->qsb;
 }

 static const QEMUFileOps buf_read_ops = {
     .get_buffer = buf_get_buffer,
     .close =      buf_close,
 };

 static const QEMUFileOps buf_write_ops = {
     .put_buffer = buf_put_buffer,
     .close =      buf_close,
 };

 QEMUFile *qemu_bufopen(const char *mode, QEMUSizedBuffer *input)
 {
     QEMUBuffer *s;

     if (mode == NULL || (mode[0] != 'r' && mode[0] != 'w') ||
         mode[1] != '\0') {
         error_report("qemu_bufopen: Argument validity check failed");
         return NULL;
     }

     s = g_new0(QEMUBuffer, 1);
     s->qsb = input;

     if (s->qsb == NULL) {
         s->qsb = qsb_create(NULL, 0);
         s->qsb_allocated = true;
     }
     if (!s->qsb) {
         g_free(s);
         error_report("qemu_bufopen: qsb_create failed");
         return NULL;
     }


     if (mode[0] == 'r') {
         s->file = qemu_fopen_ops(s, &buf_read_ops);
     } else {
         s->file = qemu_fopen_ops(s, &buf_write_ops);
     }
     return s->file;
 }
	/*
	* QEMU System Emulator
	*
	* Copyright (c) 2003-2008 Fabrice Bellard
	* Copyright (c) 2014 IBM Corp.
	*
	* Authors:
	* Stefan Berger <stefanb@linux.vnet.ibm.com>
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	* THE SOFTWARE.
	*/
	#include "qemu-common.h"
	#include "qemu/error-report.h"
	#include "qemu/iov.h"
	#include "qemu/sockets.h"
	#include "qemu/coroutine.h"
	#include "migration/migration.h"
	#include "migration/qemu-file.h"
	#include "migration/qemu-file-internal.h"
	#include "trace.h"

	#define QSB_CHUNK_SIZE (1 << 10)
	#define QSB_MAX_CHUNK_SIZE (16 * QSB_CHUNK_SIZE)

	/**
	* Create a QEMUSizedBuffer
	* This type of buffer uses scatter-gather lists internally and
	* can grow to any size. Any data array in the scatter-gather list
	* can hold different amount of bytes.
	*
	* @buffer: Optional buffer to copy into the QSB
	* @len: size of initial buffer; if @buffer is given, buffer must
	* hold at least len bytes
	*
	* Returns a pointer to a QEMUSizedBuffer or NULL on allocation failure
	*/
	QEMUSizedBuffer qsb_create(const uint8_t buffer, size_t len)
	{
	QEMUSizedBuffer *qsb;
	size_t alloc_len, num_chunks, i, to_copy;
	size_t chunk_size = (len > QSB_MAX_CHUNK_SIZE)
	? QSB_MAX_CHUNK_SIZE
	: QSB_CHUNK_SIZE;

	num_chunks = DIV_ROUND_UP(len ? len : QSB_CHUNK_SIZE, chunk_size);
	alloc_len = num_chunks * chunk_size;

	qsb = g_try_new0(QEMUSizedBuffer, 1);
	if (!qsb) {
	return NULL;
	}

	qsb->iov = g_try_new0(struct iovec, num_chunks);
	if (!qsb->iov) {
	g_free(qsb);
	return NULL;
	}

	qsb->n_iov = num_chunks;

	for (i = 0; i < num_chunks; i++) {
	qsb->iov[i].iov_base = g_try_malloc0(chunk_size);
	if (!qsb->iov[i].iov_base) {
	/* qsb_free is safe since g_free can cope with NULL */
	qsb_free(qsb);
	return NULL;
	}

	qsb->iov[i].iov_len = chunk_size;
	if (buffer) {
	to_copy = (len - qsb->used) > chunk_size
	? chunk_size : (len - qsb->used);
	memcpy(qsb->iov[i].iov_base, &buffer[qsb->used], to_copy);
	qsb->used += to_copy;
	}
	}

	qsb->size = alloc_len;

	return qsb;
	}

	/**
	* Free the QEMUSizedBuffer
	*
	* @qsb: The QEMUSizedBuffer to free
	*/
	void qsb_free(QEMUSizedBuffer *qsb)
	{
	size_t i;

	if (!qsb) {
	return;
	}

	for (i = 0; i < qsb->n_iov; i++) {
	g_free(qsb->iov[i].iov_base);
	}
	g_free(qsb->iov);
	g_free(qsb);
	}

	/**
	* Get the number of used bytes in the QEMUSizedBuffer
	*
	* @qsb: A QEMUSizedBuffer
	*
	* Returns the number of bytes currently used in this buffer
	*/
	size_t qsb_get_length(const QEMUSizedBuffer *qsb)
	{
	return qsb->used;
	}

	/**
	* Set the length of the buffer; the primary usage of this
	* function is to truncate the number of used bytes in the buffer.
	* The size will not be extended beyond the current number of
	* allocated bytes in the QEMUSizedBuffer.
	*
	* @qsb: A QEMUSizedBuffer
	* @new_len: The new length of bytes in the buffer
	*
	* Returns the number of bytes the buffer was truncated or extended
	* to.
	*/
	size_t qsb_set_length(QEMUSizedBuffer *qsb, size_t new_len)
	{
	if (new_len <= qsb->size) {
	qsb->used = new_len;
	} else {
	qsb->used = qsb->size;
	}
	return qsb->used;
	}

	/**
	* Get the iovec that holds the data for a given position @pos.
	*
	* @qsb: A QEMUSizedBuffer
	* @pos: The index of a byte in the buffer
	* @d_off: Pointer to an offset that this function will indicate
	* at what position within the returned iovec the byte
	* is to be found
	*
	* Returns the index of the iovec that holds the byte at the given
	* index @pos in the byte stream; a negative number if the iovec
	* for the given position @pos does not exist.
	*/
	static ssize_t qsb_get_iovec(const QEMUSizedBuffer *qsb,
	off_t pos, off_t *d_off)
	{
	ssize_t i;
	off_t curr = 0;

	if (pos > qsb->used) {
	return -1;
	}

	for (i = 0; i < qsb->n_iov; i++) {
	if (curr + qsb->iov[i].iov_len > pos) {
	*d_off = pos - curr;
	return i;
	}
	curr += qsb->iov[i].iov_len;
	}
	return -1;
	}

	/*
	* Convert the QEMUSizedBuffer into a flat buffer.
	*
	* Note: If at all possible, try to avoid this function since it
	* may unnecessarily copy memory around.
	*
	* @qsb: pointer to QEMUSizedBuffer
	* @start: offset to start at
	* @count: number of bytes to copy
	* @buf: a pointer to a buffer to write into (at least @count bytes)
	*
	* Returns the number of bytes copied into the output buffer
	*/
	ssize_t qsb_get_buffer(const QEMUSizedBuffer *qsb, off_t start,
	size_t count, uint8_t *buffer)
	{
	const struct iovec *iov;
	size_t to_copy, all_copy;
	ssize_t index;
	off_t s_off;
	off_t d_off = 0;
	char *s;

	if (start > qsb->used) {
	return 0;
	}

	all_copy = qsb->used - start;
	if (all_copy > count) {
	all_copy = count;
	} else {
	count = all_copy;
	}

	index = qsb_get_iovec(qsb, start, &s_off);
	if (index < 0) {
	return 0;
	}

	while (all_copy > 0) {
	iov = &qsb->iov[index];

	s = iov->iov_base;

	to_copy = iov->iov_len - s_off;
	if (to_copy > all_copy) {
	to_copy = all_copy;
	}
	memcpy(&buffer[d_off], &s[s_off], to_copy);

	d_off += to_copy;
	all_copy -= to_copy;

	s_off = 0;
	index++;
	}

	return count;
	}

	/**
	* Grow the QEMUSizedBuffer to the given size and allocate
	* memory for it.
	*
	* @qsb: A QEMUSizedBuffer
	* @new_size: The new size of the buffer
	*
	* Return:
	* a negative error code in case of memory allocation failure
	* or
	* the new size of the buffer. The returned size may be greater or equal
	* to @new_size.
	*/
	static ssize_t qsb_grow(QEMUSizedBuffer *qsb, size_t new_size)
	{
	size_t needed_chunks, i;

	if (qsb->size < new_size) {
	struct iovec *new_iov;
	size_t size_diff = new_size - qsb->size;
	size_t chunk_size = (size_diff > QSB_MAX_CHUNK_SIZE)
	? QSB_MAX_CHUNK_SIZE : QSB_CHUNK_SIZE;

	needed_chunks = DIV_ROUND_UP(size_diff, chunk_size);

	new_iov = g_try_new(struct iovec, qsb->n_iov + needed_chunks);
	if (new_iov == NULL) {
	return -ENOMEM;
	}

	/* Allocate new chunks as needed into new_iov */
	for (i = qsb->n_iov; i < qsb->n_iov + needed_chunks; i++) {
	new_iov[i].iov_base = g_try_malloc0(chunk_size);
	new_iov[i].iov_len = chunk_size;
	if (!new_iov[i].iov_base) {
	size_t j;

	/* Free previously allocated new chunks */
	for (j = qsb->n_iov; j < i; j++) {
	g_free(new_iov[j].iov_base);
	}
	g_free(new_iov);

	return -ENOMEM;
	}
	}

	/*
	* Now we can't get any allocation errors, copy over to new iov
	* and switch.
	*/
	for (i = 0; i < qsb->n_iov; i++) {
	new_iov[i] = qsb->iov[i];
	}

	qsb->n_iov += needed_chunks;
	g_free(qsb->iov);
	qsb->iov = new_iov;
	qsb->size += (needed_chunks * chunk_size);
	}

	return qsb->size;
	}

	/**
	* Write into the QEMUSizedBuffer at a given position and a given
	* number of bytes. This function will automatically grow the
	* QEMUSizedBuffer.
	*
	* @qsb: A QEMUSizedBuffer
	* @source: A byte array to copy data from
	* @pos: The position within the @qsb to write data to
	* @size: The number of bytes to copy into the @qsb
	*
	* Returns @size or a negative error code in case of memory allocation failure,
	* or with an invalid 'pos'
	*/
	ssize_t qsb_write_at(QEMUSizedBuffer qsb, const uint8_t source,
	off_t pos, size_t count)
	{
	ssize_t rc = qsb_grow(qsb, pos + count);
	size_t to_copy;
	size_t all_copy = count;
	const struct iovec *iov;
	ssize_t index;
	char *dest;
	off_t d_off, s_off = 0;

	if (rc < 0) {
	return rc;
	}

	if (pos + count > qsb->used) {
	qsb->used = pos + count;
	}

	index = qsb_get_iovec(qsb, pos, &d_off);
	if (index < 0) {
	return -EINVAL;
	}

	while (all_copy > 0) {
	iov = &qsb->iov[index];

	dest = iov->iov_base;

	to_copy = iov->iov_len - d_off;
	if (to_copy > all_copy) {
	to_copy = all_copy;
	}

	memcpy(&dest[d_off], &source[s_off], to_copy);

	s_off += to_copy;
	all_copy -= to_copy;

	d_off = 0;
	index++;
	}

	return count;
	}

	typedef struct QEMUBuffer {
	QEMUSizedBuffer *qsb;
	QEMUFile *file;
	bool qsb_allocated;
	} QEMUBuffer;

	static ssize_t buf_get_buffer(void opaque, uint8_t buf, int64_t pos,
	size_t size)
	{
	QEMUBuffer *s = opaque;
	ssize_t len = qsb_get_length(s->qsb) - pos;

	if (len <= 0) {
	return 0;
	}

	if (len > size) {
	len = size;
	}
	return qsb_get_buffer(s->qsb, pos, len, buf);
	}

	static ssize_t buf_put_buffer(void opaque, const uint8_t buf,
	int64_t pos, size_t size)
	{
	QEMUBuffer *s = opaque;

	return qsb_write_at(s->qsb, buf, pos, size);
	}

	static int buf_close(void *opaque)
	{
	QEMUBuffer *s = opaque;

	if (s->qsb_allocated) {
	qsb_free(s->qsb);
	}

	g_free(s);

	return 0;
	}

	const QEMUSizedBuffer qemu_buf_get(QEMUFile f)
	{
	QEMUBuffer *p;

	qemu_fflush(f);

	p = f->opaque;

	return p->qsb;
	}

	static const QEMUFileOps buf_read_ops = {
	.get_buffer = buf_get_buffer,
	.close = buf_close,
	};

	static const QEMUFileOps buf_write_ops = {
	.put_buffer = buf_put_buffer,
	.close = buf_close,
	};

	QEMUFile qemu_bufopen(const char mode, QEMUSizedBuffer *input)
	{
	QEMUBuffer *s;

	if (mode == NULL \|\| (mode[0] != 'r' && mode[0] != 'w') \|\|
	mode[1] != '\0') {
	error_report("qemu_bufopen: Argument validity check failed");
	return NULL;
	}

	s = g_new0(QEMUBuffer, 1);
	s->qsb = input;

	if (s->qsb == NULL) {
	s->qsb = qsb_create(NULL, 0);
	s->qsb_allocated = true;
	}
	if (!s->qsb) {
	g_free(s);
	error_report("qemu_bufopen: qsb_create failed");
	return NULL;
	}


	if (mode[0] == 'r') {
	s->file = qemu_fopen_ops(s, &buf_read_ops);
	} else {
	s->file = qemu_fopen_ops(s, &buf_write_ops);
	}
	return s->file;
	}