From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50786) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZrUOy-0001sw-BD for qemu-devel@nongnu.org; Wed, 28 Oct 2015 13:20:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZrUOu-0000zM-5Z for qemu-devel@nongnu.org; Wed, 28 Oct 2015 13:20:44 -0400 Received: from relay-05.andrew.cmu.edu ([128.2.157.12]:44027 helo=relay.andrew.cmu.edu) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZrUOt-0000z2-Mc for qemu-devel@nongnu.org; Wed, 28 Oct 2015 13:20:40 -0400 From: "Gabriel L. Somlo" Date: Wed, 28 Oct 2015 13:20:34 -0400 Message-Id: <1446052836-31737-3-git-send-email-somlo@cmu.edu> In-Reply-To: <1446052836-31737-1-git-send-email-somlo@cmu.edu> References: <1446052836-31737-1-git-send-email-somlo@cmu.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: [Qemu-devel] [PATCH v2 2/4] fw_cfg: amend callback behavior spec to once per select List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: peter.maydell@linaro.org, jordan.l.justen@intel.com, kraxel@redhat.com, pbonzini@redhat.com, markmb@redhat.com, lersek@redhat.com Currently, the fw_cfg internal API specifies that if an item was set up with a read callback, the callback must be run each time a byte is read from the item. This behavior is both wasteful (most items do not have a read callback set), and impractical for bulk transfers (e.g., DMA read). At the time of this writing, the only items configured with a callback are "/etc/table-loader", "/etc/acpi/tables", and "/etc/acpi/rsdp". They all share the same callback functions: virt_acpi_build_update() on arm (in hw/arm/virt-acpi-build.c), and acpi_build_update() on i386 (in hw/i386/acpi.c). Both of these callbacks are one-shot (i.e. they return without doing anything at all after the first time they are called on each distinct item). This patch amends the specification for fw_cfg_add_file_callback() to state that any available read callback will only be invoked once each time the item is selected. This change has no practical effect on the current behavior of QEMU, and it enables us to significantly optimize the behavior of fw_cfg reads during guest firmware setup, eliminating a large amount of redundant callback checks and invocations. Cc: Laszlo Ersek Cc: Gerd Hoffmann Cc: Marc Mar=C3=AD Signed-off-by: Gabriel Somlo --- hw/nvram/fw_cfg.c | 16 ++++++++-------- include/hw/nvram/fw_cfg.h | 8 ++------ 2 files changed, 10 insertions(+), 14 deletions(-) diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c index 73b0a81..31fa5c8 100644 --- a/hw/nvram/fw_cfg.c +++ b/hw/nvram/fw_cfg.c @@ -252,7 +252,8 @@ static void fw_cfg_write(FWCfgState *s, uint8_t value= ) =20 static int fw_cfg_select(FWCfgState *s, uint16_t key) { - int ret; + int arch, ret; + FWCfgEntry *e; =20 s->cur_offset =3D 0; if ((key & FW_CFG_ENTRY_MASK) >=3D FW_CFG_MAX_ENTRY) { @@ -261,6 +262,12 @@ static int fw_cfg_select(FWCfgState *s, uint16_t key= ) } else { s->cur_entry =3D key; ret =3D 1; + /* entry successfully selected, now run callback if present */ + arch =3D !!(key & FW_CFG_ARCH_LOCAL); + e =3D &s->entries[arch][key & FW_CFG_ENTRY_MASK]; + if (e->read_callback) { + e->read_callback(e->callback_opaque, s->cur_offset); + } } =20 trace_fw_cfg_select(s, key, ret); @@ -276,9 +283,6 @@ static uint8_t fw_cfg_read(FWCfgState *s) if (s->cur_entry =3D=3D FW_CFG_INVALID || !e->data || s->cur_offset = >=3D e->len) ret =3D 0; else { - if (e->read_callback) { - e->read_callback(e->callback_opaque, s->cur_offset); - } ret =3D e->data[s->cur_offset++]; } =20 @@ -371,10 +375,6 @@ static void fw_cfg_dma_transfer(FWCfgState *s) len =3D (e->len - s->cur_offset); } =20 - if (e->read_callback) { - e->read_callback(e->callback_opaque, s->cur_offset); - } - /* If the access is not a read access, it will be a skip acc= ess, * tested before. */ diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h index 422e2e9..47ff118 100644 --- a/include/hw/nvram/fw_cfg.h +++ b/include/hw/nvram/fw_cfg.h @@ -183,12 +183,8 @@ void fw_cfg_add_file(FWCfgState *s, const char *file= name, void *data, * structure residing at key value FW_CFG_FILE_DIR, containing the item = name, * data size, and assigned selector key value. * Additionally, set a callback function (and argument) to be called eac= h - * time a byte is read by the guest from this particular item, or once p= er - * each DMA guest read operation. - * NOTE: In addition to the opaque argument set here, the callback funct= ion - * takes the current data offset as an additional argument, allowing it = the - * option of only acting upon specific offset values (e.g., 0, before th= e - * first data byte of the selected item is returned to the guest). + * time this item is selected (by having its selector key written to the + * fw_cfg control register). */ void fw_cfg_add_file_callback(FWCfgState *s, const char *filename, FWCfgReadCallback callback, void *callback= _opaque, --=20 2.4.3