At present, the libqos/fw_cfg.c library does not support the modern DMA
interface which is required to write to the fw_cfg files. It only uses the IO
interface. Implement read and write methods based on DMA. This will enable
developers to write tests that writes to the fw_cfg file(s). The structure of
the code is taken from edk2 fw_cfg implementation. It has been tested by
writing a qtest that writes to a fw_cfg file. This test will be part of a
future patch series.

Signed-off-by: Ani Sinha <anisinha@redhat.com>
---
 tests/qtest/libqos/fw_cfg.c | 138 ++++++++++++++++++++++++++++++++++++
 tests/qtest/libqos/fw_cfg.h |   6 +-
 2 files changed, 143 insertions(+), 1 deletion(-)

diff --git a/tests/qtest/libqos/fw_cfg.c b/tests/qtest/libqos/fw_cfg.c
index f1ed4898f7..b3ae97d32d 100644
--- a/tests/qtest/libqos/fw_cfg.c
+++ b/tests/qtest/libqos/fw_cfg.c
@@ -14,6 +14,8 @@
 
 #include "qemu/osdep.h"
 #include "fw_cfg.h"
+#include "malloc-pc.h"
+#include "libqos-malloc.h"
 #include "../libqtest.h"
 #include "qemu/bswap.h"
 #include "hw/nvram/fw_cfg.h"
@@ -60,6 +62,65 @@ static void mm_fw_cfg_select(QFWCFG *fw_cfg, uint16_t key)
     qtest_writew(fw_cfg->qts, fw_cfg->base, key);
 }
 
+static void
+qfw_cfg_dma_transfer(QFWCFG *fw_cfg, QOSState *qs, void *address,
+                     uint32_t length, uint32_t control)
+{
+    FWCfgDmaAccess access;
+    uint32_t addr;
+    uint64_t guest_access_addr;
+    uint64_t gaddr;
+
+    /* create a data buffer in guest memory */
+    gaddr = guest_alloc(&qs->alloc, length);
+    g_assert(gaddr);
+
+    if (control & FW_CFG_DMA_CTL_WRITE) {
+        qtest_bufwrite(fw_cfg->qts, gaddr, address, length);
+    }
+    access.address = cpu_to_be64(gaddr);
+    access.length = cpu_to_be32(length);
+    access.control = cpu_to_be32(control);
+
+    /* now create a separate buffer in guest memory for 'access' */
+    guest_access_addr = guest_alloc(&qs->alloc, sizeof(access));
+    g_assert(guest_access_addr);
+    qtest_bufwrite(fw_cfg->qts, guest_access_addr, &access, sizeof(access));
+
+    /* write lower 32 bits of address */
+    addr = cpu_to_be32((uint32_t)(uintptr_t)guest_access_addr);
+    qtest_outl(fw_cfg->qts, fw_cfg->base + 8, addr);
+
+    /* write upper 32 bits of address */
+    addr = cpu_to_be32((uint32_t)(uintptr_t)(guest_access_addr >> 32));
+    qtest_outl(fw_cfg->qts, fw_cfg->base + 4, addr);
+
+    g_assert(!(be32_to_cpu(access.control) & FW_CFG_DMA_CTL_ERROR));
+
+    if (control & FW_CFG_DMA_CTL_READ) {
+        qtest_bufread(fw_cfg->qts, gaddr, address, length);
+    }
+
+    guest_free(&qs->alloc, guest_access_addr);
+    guest_free(&qs->alloc, gaddr);
+}
+
+static void
+qfw_cfg_write_entry(QFWCFG *fw_cfg, QOSState *qs, uint16_t key,
+                    void *buf, uint32_t len)
+{
+    qfw_cfg_select(fw_cfg, key);
+    qfw_cfg_dma_transfer(fw_cfg, qs, buf, len, FW_CFG_DMA_CTL_WRITE);
+}
+
+static void
+qfw_cfg_read_entry(QFWCFG *fw_cfg, QOSState *qs, uint16_t key,
+                   void *buf, uint32_t len)
+{
+    qfw_cfg_select(fw_cfg, key);
+    qfw_cfg_dma_transfer(fw_cfg, qs, buf, len, FW_CFG_DMA_CTL_READ);
+}
+
 static bool
 find_pdir_entry(QFWCFG *fw_cfg, const char *filename,
                 uint16_t *sel, uint32_t *size)
@@ -123,6 +184,83 @@ size_t qfw_cfg_get_file(QFWCFG *fw_cfg, const char *filename,
     return filesize;
 }
 
+/*
+ * The caller need check the return value. When the return value is
+ * nonzero, it means that some bytes have been transferred.
+ *
+ * If the fw_cfg file in question is smaller than the allocated & passed-in
+ * buffer, then the first len bytes were read.
+ *
+ * If the fw_cfg file in question is larger than the passed-in
+ * buffer, then the return value explains how much was actually read.
+ *
+ * It is illegal to call this function if fw_cfg does not support DMA
+ * interface. The caller should ensure that DMA is supported before
+ * calling this function.
+ *
+ * Passed QOSState pointer qs must be initialized. qs->alloc must also be
+ * properly initialized.
+ */
+size_t qfw_cfg_read_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
+                         void *data, size_t buflen)
+{
+    uint32_t len = 0;
+    uint16_t sel;
+    uint32_t id;
+
+    g_assert(qs);
+    /* check if DMA is supported since we use DMA for read */
+    id = qfw_cfg_get_u32(fw_cfg, FW_CFG_ID);
+    g_assert(id & FW_CFG_VERSION_DMA);
+
+    if (find_pdir_entry(fw_cfg, filename, &sel, &len)) {
+        if (len > buflen) {
+            len = buflen;
+        }
+        qfw_cfg_read_entry(fw_cfg, qs, sel, data, len);
+    }
+
+    return len;
+}
+
+/*
+ * The caller need check the return value. When the return value is
+ * nonzero, it means that some bytes have been transferred.
+ *
+ * If the fw_cfg file in question is smaller than the allocated & passed-in
+ * buffer, then the buffer has been partially written.
+ *
+ * If the fw_cfg file in question is larger than the passed-in
+ * buffer, then the return value explains how much was actually written.
+ *
+ * It is illegal to call this function if fw_cfg does not support DMA
+ * interface. The caller should ensure that DMA is supported before
+ * calling this function.
+ *
+ * Passed QOSState pointer qs must be initialized. qs->alloc must also be
+ * properly initialized.
+ */
+size_t qfw_cfg_write_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
+                          void *data, size_t buflen)
+{
+    uint32_t len = 0;
+    uint16_t sel;
+    uint32_t id;
+
+    g_assert(qs);
+    /* write operation is only valid if DMA is supported */
+    id = qfw_cfg_get_u32(fw_cfg, FW_CFG_ID);
+    g_assert(id & FW_CFG_VERSION_DMA);
+
+    if (find_pdir_entry(fw_cfg, filename, &sel, &len)) {
+        if (len > buflen) {
+            len = buflen;
+        }
+        qfw_cfg_write_entry(fw_cfg, qs, sel, data, len);
+    }
+    return len;
+}
+
 static void mm_fw_cfg_read(QFWCFG *fw_cfg, void *data, size_t len)
 {
     uint8_t *ptr = data;
diff --git a/tests/qtest/libqos/fw_cfg.h b/tests/qtest/libqos/fw_cfg.h
index b0456a15df..6d6ff09725 100644
--- a/tests/qtest/libqos/fw_cfg.h
+++ b/tests/qtest/libqos/fw_cfg.h
@@ -14,6 +14,7 @@
 #define LIBQOS_FW_CFG_H
 
 #include "../libqtest.h"
+#include "libqos.h"
 
 typedef struct QFWCFG QFWCFG;
 
@@ -33,7 +34,10 @@ uint32_t qfw_cfg_get_u32(QFWCFG *fw_cfg, uint16_t key);
 uint64_t qfw_cfg_get_u64(QFWCFG *fw_cfg, uint16_t key);
 size_t qfw_cfg_get_file(QFWCFG *fw_cfg, const char *filename,
                         void *data, size_t buflen);
-
+size_t qfw_cfg_write_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
+                          void *data, size_t buflen);
+size_t qfw_cfg_read_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
+                         void *data, size_t buflen);
 QFWCFG *mm_fw_cfg_init(QTestState *qts, uint64_t base);
 void mm_fw_cfg_uninit(QFWCFG *fw_cfg);
 QFWCFG *io_fw_cfg_init(QTestState *qts, uint16_t base);
-- 
2.45.2

Ani Sinha <anisinha@redhat.com> writes:

> At present, the libqos/fw_cfg.c library does not support the modern DMA
> interface which is required to write to the fw_cfg files. It only uses the IO
> interface. Implement read and write methods based on DMA. This will enable
> developers to write tests that writes to the fw_cfg file(s). The structure of
> the code is taken from edk2 fw_cfg implementation. It has been tested by
> writing a qtest that writes to a fw_cfg file. This test will be part of a
> future patch series.

What's the blocker for the rest of the series? It would be preferable to
merge it all together, rather than this going in first without any
users.

>
> Signed-off-by: Ani Sinha <anisinha@redhat.com>
> ---
>  tests/qtest/libqos/fw_cfg.c | 138 ++++++++++++++++++++++++++++++++++++
>  tests/qtest/libqos/fw_cfg.h |   6 +-
>  2 files changed, 143 insertions(+), 1 deletion(-)
>
> diff --git a/tests/qtest/libqos/fw_cfg.c b/tests/qtest/libqos/fw_cfg.c
> index f1ed4898f7..b3ae97d32d 100644
> --- a/tests/qtest/libqos/fw_cfg.c
> +++ b/tests/qtest/libqos/fw_cfg.c
> @@ -14,6 +14,8 @@
>  
>  #include "qemu/osdep.h"
>  #include "fw_cfg.h"
> +#include "malloc-pc.h"
> +#include "libqos-malloc.h"
>  #include "../libqtest.h"
>  #include "qemu/bswap.h"
>  #include "hw/nvram/fw_cfg.h"
> @@ -60,6 +62,65 @@ static void mm_fw_cfg_select(QFWCFG *fw_cfg, uint16_t key)
>      qtest_writew(fw_cfg->qts, fw_cfg->base, key);
>  }
>  
> +static void
> +qfw_cfg_dma_transfer(QFWCFG *fw_cfg, QOSState *qs, void *address,
> +                     uint32_t length, uint32_t control)
> +{
> +    FWCfgDmaAccess access;
> +    uint32_t addr;
> +    uint64_t guest_access_addr;
> +    uint64_t gaddr;
> +
> +    /* create a data buffer in guest memory */
> +    gaddr = guest_alloc(&qs->alloc, length);
> +    g_assert(gaddr);

Same here, none of these asserts are needed.

> +
> +    if (control & FW_CFG_DMA_CTL_WRITE) {
> +        qtest_bufwrite(fw_cfg->qts, gaddr, address, length);
> +    }
> +    access.address = cpu_to_be64(gaddr);
> +    access.length = cpu_to_be32(length);
> +    access.control = cpu_to_be32(control);
> +
> +    /* now create a separate buffer in guest memory for 'access' */
> +    guest_access_addr = guest_alloc(&qs->alloc, sizeof(access));
> +    g_assert(guest_access_addr);
> +    qtest_bufwrite(fw_cfg->qts, guest_access_addr, &access, sizeof(access));
> +
> +    /* write lower 32 bits of address */
> +    addr = cpu_to_be32((uint32_t)(uintptr_t)guest_access_addr);
> +    qtest_outl(fw_cfg->qts, fw_cfg->base + 8, addr);
> +
> +    /* write upper 32 bits of address */
> +    addr = cpu_to_be32((uint32_t)(uintptr_t)(guest_access_addr >> 32));
> +    qtest_outl(fw_cfg->qts, fw_cfg->base + 4, addr);
> +
> +    g_assert(!(be32_to_cpu(access.control) & FW_CFG_DMA_CTL_ERROR));
> +
> +    if (control & FW_CFG_DMA_CTL_READ) {
> +        qtest_bufread(fw_cfg->qts, gaddr, address, length);
> +    }
> +
> +    guest_free(&qs->alloc, guest_access_addr);
> +    guest_free(&qs->alloc, gaddr);
> +}
> +
> +static void
> +qfw_cfg_write_entry(QFWCFG *fw_cfg, QOSState *qs, uint16_t key,
> +                    void *buf, uint32_t len)
> +{
> +    qfw_cfg_select(fw_cfg, key);
> +    qfw_cfg_dma_transfer(fw_cfg, qs, buf, len, FW_CFG_DMA_CTL_WRITE);
> +}
> +
> +static void
> +qfw_cfg_read_entry(QFWCFG *fw_cfg, QOSState *qs, uint16_t key,
> +                   void *buf, uint32_t len)
> +{
> +    qfw_cfg_select(fw_cfg, key);
> +    qfw_cfg_dma_transfer(fw_cfg, qs, buf, len, FW_CFG_DMA_CTL_READ);
> +}
> +
>  static bool
>  find_pdir_entry(QFWCFG *fw_cfg, const char *filename,
>                  uint16_t *sel, uint32_t *size)
> @@ -123,6 +184,83 @@ size_t qfw_cfg_get_file(QFWCFG *fw_cfg, const char *filename,
>      return filesize;
>  }
>  
> +/*
> + * The caller need check the return value. When the return value is
> + * nonzero, it means that some bytes have been transferred.
> + *
> + * If the fw_cfg file in question is smaller than the allocated & passed-in
> + * buffer, then the first len bytes were read.
> + *
> + * If the fw_cfg file in question is larger than the passed-in
> + * buffer, then the return value explains how much was actually read.
> + *
> + * It is illegal to call this function if fw_cfg does not support DMA
> + * interface. The caller should ensure that DMA is supported before
> + * calling this function.
> + *
> + * Passed QOSState pointer qs must be initialized. qs->alloc must also be
> + * properly initialized.
> + */
> +size_t qfw_cfg_read_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
> +                         void *data, size_t buflen)
> +{
> +    uint32_t len = 0;
> +    uint16_t sel;
> +    uint32_t id;
> +
> +    g_assert(qs);
> +    /* check if DMA is supported since we use DMA for read */
> +    id = qfw_cfg_get_u32(fw_cfg, FW_CFG_ID);
> +    g_assert(id & FW_CFG_VERSION_DMA);
> +
> +    if (find_pdir_entry(fw_cfg, filename, &sel, &len)) {
> +        if (len > buflen) {
> +            len = buflen;
> +        }
> +        qfw_cfg_read_entry(fw_cfg, qs, sel, data, len);
> +    }
> +
> +    return len;
> +}
> +
> +/*
> + * The caller need check the return value. When the return value is
> + * nonzero, it means that some bytes have been transferred.
> + *
> + * If the fw_cfg file in question is smaller than the allocated & passed-in
> + * buffer, then the buffer has been partially written.
> + *
> + * If the fw_cfg file in question is larger than the passed-in
> + * buffer, then the return value explains how much was actually written.
> + *
> + * It is illegal to call this function if fw_cfg does not support DMA
> + * interface. The caller should ensure that DMA is supported before
> + * calling this function.
> + *
> + * Passed QOSState pointer qs must be initialized. qs->alloc must also be
> + * properly initialized.
> + */
> +size_t qfw_cfg_write_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
> +                          void *data, size_t buflen)
> +{
> +    uint32_t len = 0;
> +    uint16_t sel;
> +    uint32_t id;
> +
> +    g_assert(qs);
> +    /* write operation is only valid if DMA is supported */
> +    id = qfw_cfg_get_u32(fw_cfg, FW_CFG_ID);
> +    g_assert(id & FW_CFG_VERSION_DMA);
> +
> +    if (find_pdir_entry(fw_cfg, filename, &sel, &len)) {
> +        if (len > buflen) {
> +            len = buflen;
> +        }
> +        qfw_cfg_write_entry(fw_cfg, qs, sel, data, len);
> +    }
> +    return len;
> +}
> +
>  static void mm_fw_cfg_read(QFWCFG *fw_cfg, void *data, size_t len)
>  {
>      uint8_t *ptr = data;
> diff --git a/tests/qtest/libqos/fw_cfg.h b/tests/qtest/libqos/fw_cfg.h
> index b0456a15df..6d6ff09725 100644
> --- a/tests/qtest/libqos/fw_cfg.h
> +++ b/tests/qtest/libqos/fw_cfg.h
> @@ -14,6 +14,7 @@
>  #define LIBQOS_FW_CFG_H
>  
>  #include "../libqtest.h"
> +#include "libqos.h"
>  
>  typedef struct QFWCFG QFWCFG;
>  
> @@ -33,7 +34,10 @@ uint32_t qfw_cfg_get_u32(QFWCFG *fw_cfg, uint16_t key);
>  uint64_t qfw_cfg_get_u64(QFWCFG *fw_cfg, uint16_t key);
>  size_t qfw_cfg_get_file(QFWCFG *fw_cfg, const char *filename,
>                          void *data, size_t buflen);
> -
> +size_t qfw_cfg_write_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
> +                          void *data, size_t buflen);
> +size_t qfw_cfg_read_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
> +                         void *data, size_t buflen);
>  QFWCFG *mm_fw_cfg_init(QTestState *qts, uint64_t base);
>  void mm_fw_cfg_uninit(QFWCFG *fw_cfg);
>  QFWCFG *io_fw_cfg_init(QTestState *qts, uint16_t base);

On 9/1/25 21:30, Fabiano Rosas wrote:
> Ani Sinha <anisinha@redhat.com> writes:
> 
>> At present, the libqos/fw_cfg.c library does not support the modern DMA
>> interface which is required to write to the fw_cfg files. It only uses the IO
>> interface. Implement read and write methods based on DMA. This will enable
>> developers to write tests that writes to the fw_cfg file(s). The structure of
>> the code is taken from edk2 fw_cfg implementation. It has been tested by
>> writing a qtest that writes to a fw_cfg file. This test will be part of a
>> future patch series.
> 
> What's the blocker for the rest of the series? It would be preferable to
> merge it all together, rather than this going in first without any
> users.

Agreed. We could use a multiboot image, or a guest with vmcoreinfo
support. Or a dumbier test just testing this API.

>>
>> Signed-off-by: Ani Sinha <anisinha@redhat.com>
>> ---
>>   tests/qtest/libqos/fw_cfg.c | 138 ++++++++++++++++++++++++++++++++++++
>>   tests/qtest/libqos/fw_cfg.h |   6 +-
>>   2 files changed, 143 insertions(+), 1 deletion(-)

> On 10 Jan 2025, at 2:00 AM, Fabiano Rosas <farosas@suse.de> wrote:
> 
> Ani Sinha <anisinha@redhat.com> writes:
> 
>> At present, the libqos/fw_cfg.c library does not support the modern DMA
>> interface which is required to write to the fw_cfg files. It only uses the IO
>> interface. Implement read and write methods based on DMA. This will enable
>> developers to write tests that writes to the fw_cfg file(s). The structure of
>> the code is taken from edk2 fw_cfg implementation. It has been tested by
>> writing a qtest that writes to a fw_cfg file. This test will be part of a
>> future patch series.
> 
> What's the blocker for the rest of the series?

The broker is that the consumer of this api is a new qtest which is written to test a brand new feature. I would rather post that patchset separately.
A compromise is ... 

> It would be preferable to
> merge it all together, rather than this going in first without any
> users.

In my cover letter I have pointed to the patch series that actually uses this api. That way those who want to check out that branch and test these changes can do so.

> 
>> 
>> Signed-off-by: Ani Sinha <anisinha@redhat.com>
>> ---
>> tests/qtest/libqos/fw_cfg.c | 138 ++++++++++++++++++++++++++++++++++++
>> tests/qtest/libqos/fw_cfg.h |   6 +-
>> 2 files changed, 143 insertions(+), 1 deletion(-)
>> 
>> diff --git a/tests/qtest/libqos/fw_cfg.c b/tests/qtest/libqos/fw_cfg.c
>> index f1ed4898f7..b3ae97d32d 100644
>> --- a/tests/qtest/libqos/fw_cfg.c
>> +++ b/tests/qtest/libqos/fw_cfg.c
>> @@ -14,6 +14,8 @@
>> 
>> #include "qemu/osdep.h"
>> #include "fw_cfg.h"
>> +#include "malloc-pc.h"
>> +#include "libqos-malloc.h"
>> #include "../libqtest.h"
>> #include "qemu/bswap.h"
>> #include "hw/nvram/fw_cfg.h"
>> @@ -60,6 +62,65 @@ static void mm_fw_cfg_select(QFWCFG *fw_cfg, uint16_t key)
>>     qtest_writew(fw_cfg->qts, fw_cfg->base, key);
>> }
>> 
>> +static void
>> +qfw_cfg_dma_transfer(QFWCFG *fw_cfg, QOSState *qs, void *address,
>> +                     uint32_t length, uint32_t control)
>> +{
>> +    FWCfgDmaAccess access;
>> +    uint32_t addr;
>> +    uint64_t guest_access_addr;
>> +    uint64_t gaddr;
>> +
>> +    /* create a data buffer in guest memory */
>> +    gaddr = guest_alloc(&qs->alloc, length);
>> +    g_assert(gaddr);
> 
> Same here, none of these asserts are needed.

Ok will remove.

> 
>> +
>> +    if (control & FW_CFG_DMA_CTL_WRITE) {
>> +        qtest_bufwrite(fw_cfg->qts, gaddr, address, length);
>> +    }
>> +    access.address = cpu_to_be64(gaddr);
>> +    access.length = cpu_to_be32(length);
>> +    access.control = cpu_to_be32(control);
>> +
>> +    /* now create a separate buffer in guest memory for 'access' */
>> +    guest_access_addr = guest_alloc(&qs->alloc, sizeof(access));
>> +    g_assert(guest_access_addr);
>> +    qtest_bufwrite(fw_cfg->qts, guest_access_addr, &access, sizeof(access));
>> +
>> +    /* write lower 32 bits of address */
>> +    addr = cpu_to_be32((uint32_t)(uintptr_t)guest_access_addr);
>> +    qtest_outl(fw_cfg->qts, fw_cfg->base + 8, addr);
>> +
>> +    /* write upper 32 bits of address */
>> +    addr = cpu_to_be32((uint32_t)(uintptr_t)(guest_access_addr >> 32));
>> +    qtest_outl(fw_cfg->qts, fw_cfg->base + 4, addr);
>> +
>> +    g_assert(!(be32_to_cpu(access.control) & FW_CFG_DMA_CTL_ERROR));
>> +
>> +    if (control & FW_CFG_DMA_CTL_READ) {
>> +        qtest_bufread(fw_cfg->qts, gaddr, address, length);
>> +    }
>> +
>> +    guest_free(&qs->alloc, guest_access_addr);
>> +    guest_free(&qs->alloc, gaddr);
>> +}
>> +
>> +static void
>> +qfw_cfg_write_entry(QFWCFG *fw_cfg, QOSState *qs, uint16_t key,
>> +                    void *buf, uint32_t len)
>> +{
>> +    qfw_cfg_select(fw_cfg, key);
>> +    qfw_cfg_dma_transfer(fw_cfg, qs, buf, len, FW_CFG_DMA_CTL_WRITE);
>> +}
>> +
>> +static void
>> +qfw_cfg_read_entry(QFWCFG *fw_cfg, QOSState *qs, uint16_t key,
>> +                   void *buf, uint32_t len)
>> +{
>> +    qfw_cfg_select(fw_cfg, key);
>> +    qfw_cfg_dma_transfer(fw_cfg, qs, buf, len, FW_CFG_DMA_CTL_READ);
>> +}
>> +
>> static bool
>> find_pdir_entry(QFWCFG *fw_cfg, const char *filename,
>>                 uint16_t *sel, uint32_t *size)
>> @@ -123,6 +184,83 @@ size_t qfw_cfg_get_file(QFWCFG *fw_cfg, const char *filename,
>>     return filesize;
>> }
>> 
>> +/*
>> + * The caller need check the return value. When the return value is
>> + * nonzero, it means that some bytes have been transferred.
>> + *
>> + * If the fw_cfg file in question is smaller than the allocated & passed-in
>> + * buffer, then the first len bytes were read.
>> + *
>> + * If the fw_cfg file in question is larger than the passed-in
>> + * buffer, then the return value explains how much was actually read.
>> + *
>> + * It is illegal to call this function if fw_cfg does not support DMA
>> + * interface. The caller should ensure that DMA is supported before
>> + * calling this function.
>> + *
>> + * Passed QOSState pointer qs must be initialized. qs->alloc must also be
>> + * properly initialized.
>> + */
>> +size_t qfw_cfg_read_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
>> +                         void *data, size_t buflen)
>> +{
>> +    uint32_t len = 0;
>> +    uint16_t sel;
>> +    uint32_t id;
>> +
>> +    g_assert(qs);
>> +    /* check if DMA is supported since we use DMA for read */
>> +    id = qfw_cfg_get_u32(fw_cfg, FW_CFG_ID);
>> +    g_assert(id & FW_CFG_VERSION_DMA);
>> +
>> +    if (find_pdir_entry(fw_cfg, filename, &sel, &len)) {
>> +        if (len > buflen) {
>> +            len = buflen;
>> +        }
>> +        qfw_cfg_read_entry(fw_cfg, qs, sel, data, len);
>> +    }
>> +
>> +    return len;
>> +}
>> +
>> +/*
>> + * The caller need check the return value. When the return value is
>> + * nonzero, it means that some bytes have been transferred.
>> + *
>> + * If the fw_cfg file in question is smaller than the allocated & passed-in
>> + * buffer, then the buffer has been partially written.
>> + *
>> + * If the fw_cfg file in question is larger than the passed-in
>> + * buffer, then the return value explains how much was actually written.
>> + *
>> + * It is illegal to call this function if fw_cfg does not support DMA
>> + * interface. The caller should ensure that DMA is supported before
>> + * calling this function.
>> + *
>> + * Passed QOSState pointer qs must be initialized. qs->alloc must also be
>> + * properly initialized.
>> + */
>> +size_t qfw_cfg_write_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
>> +                          void *data, size_t buflen)
>> +{
>> +    uint32_t len = 0;
>> +    uint16_t sel;
>> +    uint32_t id;
>> +
>> +    g_assert(qs);
>> +    /* write operation is only valid if DMA is supported */
>> +    id = qfw_cfg_get_u32(fw_cfg, FW_CFG_ID);
>> +    g_assert(id & FW_CFG_VERSION_DMA);
>> +
>> +    if (find_pdir_entry(fw_cfg, filename, &sel, &len)) {
>> +        if (len > buflen) {
>> +            len = buflen;
>> +        }
>> +        qfw_cfg_write_entry(fw_cfg, qs, sel, data, len);
>> +    }
>> +    return len;
>> +}
>> +
>> static void mm_fw_cfg_read(QFWCFG *fw_cfg, void *data, size_t len)
>> {
>>     uint8_t *ptr = data;
>> diff --git a/tests/qtest/libqos/fw_cfg.h b/tests/qtest/libqos/fw_cfg.h
>> index b0456a15df..6d6ff09725 100644
>> --- a/tests/qtest/libqos/fw_cfg.h
>> +++ b/tests/qtest/libqos/fw_cfg.h
>> @@ -14,6 +14,7 @@
>> #define LIBQOS_FW_CFG_H
>> 
>> #include "../libqtest.h"
>> +#include "libqos.h"
>> 
>> typedef struct QFWCFG QFWCFG;
>> 
>> @@ -33,7 +34,10 @@ uint32_t qfw_cfg_get_u32(QFWCFG *fw_cfg, uint16_t key);
>> uint64_t qfw_cfg_get_u64(QFWCFG *fw_cfg, uint16_t key);
>> size_t qfw_cfg_get_file(QFWCFG *fw_cfg, const char *filename,
>>                         void *data, size_t buflen);
>> -
>> +size_t qfw_cfg_write_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
>> +                          void *data, size_t buflen);
>> +size_t qfw_cfg_read_file(QFWCFG *fw_cfg, QOSState *qs, const char *filename,
>> +                         void *data, size_t buflen);
>> QFWCFG *mm_fw_cfg_init(QTestState *qts, uint64_t base);
>> void mm_fw_cfg_uninit(QFWCFG *fw_cfg);
>> QFWCFG *io_fw_cfg_init(QTestState *qts, uint16_t base);

On Fri, Jan 10, 2025 at 10:53:32AM +0530, Ani Sinha wrote:
> 
> 
> > On 10 Jan 2025, at 2:00 AM, Fabiano Rosas <farosas@suse.de> wrote:
> > 
> > Ani Sinha <anisinha@redhat.com> writes:
> > 
> >> At present, the libqos/fw_cfg.c library does not support the modern DMA
> >> interface which is required to write to the fw_cfg files. It only uses the IO
> >> interface. Implement read and write methods based on DMA. This will enable
> >> developers to write tests that writes to the fw_cfg file(s). The structure of
> >> the code is taken from edk2 fw_cfg implementation. It has been tested by
> >> writing a qtest that writes to a fw_cfg file. This test will be part of a
> >> future patch series.
> > 
> > What's the blocker for the rest of the series?
> 
> The broker is that the consumer of this api is a new qtest which is written to test a brand new feature.

A in-tree user of fw_cfg file writes is ramfb, so writing a ramfb test
would be an option ...

take care,
  Gerd