chardev: Allow setting file chardev input file on the command line

Our 'file' chardev backend supports both "output from this chardev
is written to a file" and "input from this chardev should be read
from a file" (except on Windows). However, you can only set up
the input file if you're using the QMP interface -- there is no
command line syntax to do it.

Add command line syntax to allow specifying an input file
as well as an output file, using a new 'input-path' suboption.

The specific use case I have is that I'd like to be able to
feed fuzzer reproducer input into qtest without having to use
'-qtest stdio' and put the input onto stdin. Being able to
use a file chardev like this:
 -chardev file,id=repro,path=/dev/null,input-path=repro.txt -qtest chardev:repro
means that stdio is free for use by gdb.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20230413150724.404304-3-peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
[thuth: Replace "input-file=" typo with "input-path="]
Signed-off-by: Thomas Huth <thuth@redhat.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/chardev/char-file.c b/chardev/char-file.c
index 3a7b9caf6f..263e6da563 100644
--- a/chardev/char-file.c
+++ b/chardev/char-file.c
@@ -100,6 +100,7 @@ static void qemu_chr_parse_file_out(QemuOpts *opts, ChardevBackend *backend,
                                     Error **errp)
 {
     const char *path = qemu_opt_get(opts, "path");
+    const char *inpath = qemu_opt_get(opts, "input-path");
     ChardevFile *file;
 
     backend->type = CHARDEV_BACKEND_KIND_FILE;
@@ -107,9 +108,16 @@ static void qemu_chr_parse_file_out(QemuOpts *opts, ChardevBackend *backend,
         error_setg(errp, "chardev: file: no filename given");
         return;
     }
+#ifdef _WIN32
+    if (inpath) {
+        error_setg(errp, "chardev: file: input-path not supported on Windows");
+        return;
+    }
+#endif
     file = backend->u.file.data = g_new0(ChardevFile, 1);
     qemu_chr_parse_common(opts, qapi_ChardevFile_base(file));
     file->out = g_strdup(path);
+    file->in = g_strdup(inpath);
 
     file->has_append = true;
     file->append = qemu_opt_get_bool(opts, "append", false);