On Thu, 11 Nov 2010 17:32:06 +0100 Markus Armbruster <arm...@redhat.com> wrote:
> Luiz Capitulino <lcapitul...@redhat.com> writes: > > > On Thu, 11 Nov 2010 16:30:26 +0100 > > Markus Armbruster <arm...@redhat.com> wrote: > > > >> Luiz Capitulino <lcapitul...@redhat.com> writes: > >> > >> > This driver handles in-memory chardev operations. That's, all writes > >> > to this driver are stored in an internal buffer and it doesn't talk > >> > to the external world in any way. > >> > > >> > Right now it's very simple: it supports only writes. But it can be > >> > easily extended to support more operations. > >> > > >> > This is going to be used by the monitor's "HMP passthrough via QMP" > >> > feature, which needs to run monitor handlers without a backing > >> > device. > >> > > >> > Signed-off-by: Luiz Capitulino <lcapitul...@redhat.com> > >> > --- > >> > qemu-char.c | 66 > >> > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > >> > qemu-char.h | 6 +++++ > >> > 2 files changed, 72 insertions(+), 0 deletions(-) > >> > > >> > diff --git a/qemu-char.c b/qemu-char.c > >> > index 88997f9..896df14 100644 > >> > --- a/qemu-char.c > >> > +++ b/qemu-char.c > >> > @@ -2275,6 +2275,72 @@ static CharDriverState > >> > *qemu_chr_open_socket(QemuOpts *opts) > >> > return NULL; > >> > } > >> > > >> > +/***********************************************************/ > >> > +/* Memory chardev */ > >> > +typedef struct { > >> > + size_t outbuf_size; > >> > + size_t outbuf_capacity; > >> > + uint8_t *outbuf; > >> > +} MemoryDriver; > >> > + > >> > +static int mem_chr_write(CharDriverState *chr, const uint8_t *buf, int > >> > len) > >> > +{ > >> > + MemoryDriver *d = chr->opaque; > >> > + > >> > + /* TODO: the QString implementation has the same code, we should > >> > + * introduce a generic way to do this in cutils.c */ > >> > + if (d->outbuf_capacity < d->outbuf_size + len) { > >> > + /* grown outbuf */ > >> > >> Used to say "grow" (sans n) here. Intentional change? > > > > Hum, no. I think I've squashed an older commit while rebasing (but this > > seems > > to be the only problem). > > > >> > >> > + d->outbuf_capacity += len; > >> > + d->outbuf_capacity *= 2; > >> > + d->outbuf = qemu_realloc(d->outbuf, d->outbuf_capacity); > >> > + } > >> > + > >> > + memcpy(d->outbuf + d->outbuf_size, buf, len); > >> > + d->outbuf_size += len; > >> > + > >> > + return len; > >> > +} > >> > + > >> > +#define DEFAULT_BUF_SIZE 4096 > >> > >> It's the *initial* buffer size, isn't it? > > > > Yes. > > Could we make the name reflect that then? > > >> Doubt it's worth a #define (there's just one user), but that's a matter > >> of taste. > >> > >> > + > >> > +void qemu_chr_init_mem(CharDriverState *chr) > >> > +{ > >> > + MemoryDriver *d; > >> > + > >> > + d = qemu_malloc(sizeof(*d)); > >> > + d->outbuf_size = 0; > >> > + d->outbuf_capacity = DEFAULT_BUF_SIZE; > >> > + d->outbuf = qemu_mallocz(d->outbuf_capacity); > >> > + > >> > + memset(chr, 0, sizeof(*chr)); > >> > + chr->opaque = d; > >> > + chr->chr_write = mem_chr_write; > >> > +} > >> > + > >> > +/* assumes the stored data is a string */ > >> > >> What else could it be? Worrying about embedded '\0's? > > > > Yes, as the driver itself doesn't interpret the contents of its > > buffer. > > What happens if there are embedded '\0's? The string will be shorter than expected? And what if it contains non-printable characters? It's just a cautionary comment to help the user identify such problems, I think we're making a whole argument about a quite minor thing. > > >> > +QString *qemu_chr_mem_to_qs(CharDriverState *chr) > >> > +{ > >> > + MemoryDriver *d = chr->opaque; > >> > + > >> > + if (d->outbuf_size == 0) { > >> > + return NULL; > >> > + } > >> > >> Did you forget to change this? We agreed to return an empty QString > >> when chr contains an empty string. > > > > I've changed my mind and forgot to mention it: I thought that we would > > need to return NULL on error conditions, but turns out that this function > > never fails. > > > > So, I do think it's better to let it that way for two reasons: > > > > 1. An empty has at least the '\0' character, but in this case the buffer > > is really empty > > qstring_from_substr() copies the contents of the buffer (any length > works, including 0), then appends a '\0'. I'm afraid I don't get the > problem here... > > > 2. Returning an empty string for this case will add unneeded complexity > > to the caller, ie. checking if the QString's length is 0 and decref'ing > > it > > I strongly recommend not to screw up the interface of a generally useful > function like qemu_chr_mem_to_qs() just to make its initial user > marginally simpler. Okay, found a different way of doing this that should make us both happy. Very exciting changes in v3! > > If you decide not to follow my recommendation, please document the > unusual mapping of empty string to null pointer in a function comment. > > >> > + > >> > + return qstring_from_substr((char *) d->outbuf, 0, d->outbuf_size - > >> > 1); > >> > +} > >> > + > >> > +/* NOTE: this driver can not be closed with qemu_chr_close()! */ > >> > +void qemu_chr_close_mem(CharDriverState *chr) > >> > +{ > >> > + MemoryDriver *d = chr->opaque; > >> > + > >> > + qemu_free(d->outbuf); > >> > + qemu_free(chr->opaque); > >> > + chr->opaque = NULL; > >> > + chr->chr_write = NULL; > >> > +} > >> > + > >> > >> Unlike normal character drivers, this one can't be closed with > >> qemu_chr_close(). It probably explodes if you try. Please add a > >> suitable assertion to qemu_chr_close() to document the fact, and to > >> ensure misuse fails in a controlled, obvious manner. > > > > Ah forgot, but that can be done as a separate patch, so if I don't respin > > this series I'll send an additional patch for that. > > Okay. Btw, what should we assert() for? We're going to have to access QTAILQ member I guess. > > >> > >> > QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename) > >> > { > >> > char host[65], port[33], width[8], height[8]; > >> > diff --git a/qemu-char.h b/qemu-char.h > >> > index 18ad12b..c4e55b4 100644 > >> > --- a/qemu-char.h > >> > +++ b/qemu-char.h > >> > @@ -6,6 +6,7 @@ > >> > #include "qemu-option.h" > >> > #include "qemu-config.h" > >> > #include "qobject.h" > >> > +#include "qstring.h" > >> > > >> > /* character device */ > >> > > >> > @@ -100,6 +101,11 @@ CharDriverState *qemu_chr_open_eventfd(int eventfd); > >> > > >> > extern int term_escape_char; > >> > > >> > +/* memory chardev */ > >> > +void qemu_chr_init_mem(CharDriverState *chr); > >> > +void qemu_chr_close_mem(CharDriverState *chr); > >> > +QString *qemu_chr_mem_to_qs(CharDriverState *chr); > >> > + > >> > /* async I/O support */ > >> > > >> > int qemu_set_fd_handler2(int fd, > >> >