On 19/06/21 00:27, Jing Zhang wrote:
+/**
+ * kvm_stats_read() - Common vm/vcpu stats read function to userspace.
Common function to read from the binary statistics file descriptor.
+ * @id: identification string of the stats
+ * @header: stats header for a vm or a vcpu
+ * @desc: start address of an array of stats descriptors for a vm or a vcpu
+ * @stats: start address of stats data block for a vm or a vcpu
+ * @size_stats: the size of stats data block pointed by @stats
+ * @user_buffer: start address of userspace buffer
+ * @size: requested read size from userspace
+ * @offset: the start position from which the content will be read for the
+ * corresponding vm or vcp file descriptor
+ *
+ * The file content of a vm/vcpu file descriptor is now defined as below:
+ * +-------------+
+ * | Header |
+ * +-------------+
+ * | id string |
+ * +-------------+
+ * | Descriptors |
+ * +-------------+
+ * | Stats Data |
+ * +-------------+
+ * Although this function allows userspace to read any amount of data (as long
+ * as in the limit) from any position, the typical usage would follow below
+ * steps:
+ * 1. Read header from offset 0. Get the offset of descriptors and stats data
+ * and some other necessary information. This is a one-time work for the
+ * lifecycle of the corresponding vm/vcpu stats fd.
+ * 2. Read id string from its offset. This is a one-time work for the lifecycle
+ * of the corresponding vm/vcpu stats fd.
+ * 3. Read descriptors from its offset and discover all the stats by parsing
+ * descriptors. This is a one-time work for the lifecycle of the
+ * corresponding vm/vcpu stats fd.
+ * 4. Periodically read stats data from its offset using pread.
+ *
+ * Return: the number of bytes that has been successfully read
+ */
+ssize_t kvm_stats_read(char *id, const struct kvm_stats_header *header,
+ const struct _kvm_stats_desc *desc,
+ void *stats, size_t size_stats,
+ char __user *user_buffer, size_t size, loff_t *offset)
You can replace the header argument with just the number of descriptors,
and then construct the header in the "if" statement below that copies it
to userspace:
const struct kvm_stats_header kvm_vm_stats_header = {
.name_size = KVM_STATS_NAME_SIZE,
.num_desc = num_desc,
.id_offset = size_header,
.desc_offset = size_header + KVM_STATS_NAME_SIZE,
.data_offset = size_header + KVM_STATS_NAME_SIZE +
size_desc,
};
Of course size_header can be assigned with sizeof (struct kvm_stats_header).
This removes the definition of the header in each architecture.
Paolo
+{
+ ssize_t len;
+ ssize_t copylen;
+ ssize_t remain = size;
+ size_t size_desc;
+ size_t size_header;
+ void *src;
+ loff_t pos = *offset;
+ char __user *dest = user_buffer;
+
+ size_header = sizeof(*header);
+ size_desc = header->num_desc * sizeof(*desc);
+
+ len = KVM_STATS_NAME_SIZE + size_header + size_desc + size_stats - pos;
+ len = min(len, remain);
+ if (len <= 0)
+ return 0;
+ remain = len;
+
+ /*
+ * Copy kvm stats header.
+ * The header is the first block of content userspace usually read out.
+ * The pos is 0 and the copylen and remain would be the size of header.
+ * The copy of the header would be skipped if offset is larger than the
+ * size of header. That usually happens when userspace reads stats
+ * descriptors and stats data.
+ */
+ copylen = size_header - pos;
+ copylen = min(copylen, remain);
+ if (copylen > 0) {
+ src = (void *)header + pos;
+ if (copy_to_user(dest, src, copylen))
+ return -EFAULT;
+ remain -= copylen;
+ pos += copylen;
+ dest += copylen;
+ }
+
+ /*
+ * Copy kvm stats header id string.
+ * The id string is unique for every vm/vcpu, which is stored in kvm
+ * and kvm_vcpu structure.
+ * The id string is part of the stat header from the perspective of
+ * userspace, it is usually read out together with previous constant
+ * header part and could be skipped for later descriptors and stats
+ * data readings.
+ */
+ copylen = size_header + KVM_STATS_NAME_SIZE - pos;
Should use header->id_offset instead of size_header here and in the
computation of src.
+ copylen = min(copylen, remain);
+ if (copylen > 0) {
+ src = id + pos - size_header;
+ if (copy_to_user(dest, src, copylen))
+ return -EFAULT;
+ remain -= copylen;
+ pos += copylen;
+ dest += copylen;
+ }
+
+ /*
+ * Copy kvm stats descriptors.
+ * The descriptors copy would be skipped in the typical case that
+ * userspace periodically read stats data, since the pos would be
+ * greater than the end address of descriptors
+ * (header->header.desc_offset + size_desc) causing copylen <= 0.
+ */
+ copylen = header->desc_offset + size_desc - pos;
+ copylen = min(copylen, remain);
+ if (copylen > 0) {
+ src = (void *)desc + pos - header->desc_offset;
+ if (copy_to_user(dest, src, copylen))
+ return -EFAULT;
+ remain -= copylen;
+ pos += copylen;
+ dest += copylen;
+ }
+
+ /* Copy kvm stats values */
+ copylen = header->data_offset + size_stats - pos;
+ copylen = min(copylen, remain);
+ if (copylen > 0) {
+ src = stats + pos - header->data_offset;
+ if (copy_to_user(dest, src, copylen))
+ return -EFAULT;
+ remain -= copylen;
+ pos += copylen;
+ dest += copylen;
+ }
+
+ *offset = pos;
+ return len;
+}
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