diff options
| -rw-r--r-- | include/migration/qemu-file.h | 5 | ||||
| -rw-r--r-- | qemu-file.c | 53 |
2 files changed, 54 insertions, 4 deletions
diff --git a/include/migration/qemu-file.h b/include/migration/qemu-file.h index a191fb6d8d..c90f5298ab 100644 --- a/include/migration/qemu-file.h +++ b/include/migration/qemu-file.h @@ -123,6 +123,11 @@ void qemu_put_be32(QEMUFile *f, unsigned int v); void qemu_put_be64(QEMUFile *f, uint64_t v); int qemu_peek_buffer(QEMUFile *f, uint8_t *buf, int size, size_t offset); int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int size); +/* + * Note that you can only peek continuous bytes from where the current pointer + * is; you aren't guaranteed to be able to peak to +n bytes unless you've + * previously peeked +n-1. + */ int qemu_peek_byte(QEMUFile *f, int offset); int qemu_get_byte(QEMUFile *f); void qemu_file_skip(QEMUFile *f, int size); diff --git a/qemu-file.c b/qemu-file.c index 8d5f45dcb0..a8e39127f2 100644 --- a/qemu-file.c +++ b/qemu-file.c @@ -530,7 +530,15 @@ size_t ram_control_save_page(QEMUFile *f, ram_addr_t block_offset, return RAM_SAVE_CONTROL_NOT_SUPP; } -static void qemu_fill_buffer(QEMUFile *f) +/* + * Attempt to fill the buffer from the underlying file + * Returns the number of bytes read, or negative value for an error. + * + * Note that it can return a partially full buffer even in a not error/not EOF + * case if the underlying file descriptor gives a short read, and that can + * happen even on a blocking fd. + */ +static ssize_t qemu_fill_buffer(QEMUFile *f) { int len; int pending; @@ -554,6 +562,8 @@ static void qemu_fill_buffer(QEMUFile *f) } else if (len != -EAGAIN) { qemu_file_set_error(f, len); } + + return len; } int qemu_get_fd(QEMUFile *f) @@ -685,17 +695,39 @@ void qemu_file_skip(QEMUFile *f, int size) } } +/* + * Read 'size' bytes from file (at 'offset') into buf without moving the + * pointer. + * + * It will return size bytes unless there was an error, in which case it will + * return as many as it managed to read (assuming blocking fd's which + * all current QEMUFile are) + */ int qemu_peek_buffer(QEMUFile *f, uint8_t *buf, int size, size_t offset) { int pending; int index; assert(!qemu_file_is_writable(f)); + assert(offset < IO_BUF_SIZE); + assert(size <= IO_BUF_SIZE - offset); + /* The 1st byte to read from */ index = f->buf_index + offset; + /* The number of available bytes starting at index */ pending = f->buf_size - index; - if (pending < size) { - qemu_fill_buffer(f); + + /* + * qemu_fill_buffer might return just a few bytes, even when there isn't + * an error, so loop collecting them until we get enough. + */ + while (pending < size) { + int received = qemu_fill_buffer(f); + + if (received <= 0) { + break; + } + index = f->buf_index + offset; pending = f->buf_size - index; } @@ -711,6 +743,14 @@ int qemu_peek_buffer(QEMUFile *f, uint8_t *buf, int size, size_t offset) return size; } +/* + * Read 'size' bytes of data from the file into buf. + * 'size' can be larger than the internal buffer. + * + * It will return size bytes unless there was an error, in which case it will + * return as many as it managed to read (assuming blocking fd's which + * all current QEMUFile are) + */ int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int size) { int pending = size; @@ -719,7 +759,7 @@ int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int size) while (pending > 0) { int res; - res = qemu_peek_buffer(f, buf, pending, 0); + res = qemu_peek_buffer(f, buf, MIN(pending, IO_BUF_SIZE), 0); if (res == 0) { return done; } @@ -731,11 +771,16 @@ int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int size) return done; } +/* + * Peeks a single byte from the buffer; this isn't guaranteed to work if + * offset leaves a gap after the previous read/peeked data. + */ int qemu_peek_byte(QEMUFile *f, int offset) { int index = f->buf_index + offset; assert(!qemu_file_is_writable(f)); + assert(offset < IO_BUF_SIZE); if (index >= f->buf_size) { qemu_fill_buffer(f); |