diff options
Diffstat (limited to 'virt')
| -rw-r--r-- | virt/kvm/binary_stats.c | 146 |
1 files changed, 146 insertions, 0 deletions
diff --git a/virt/kvm/binary_stats.c b/virt/kvm/binary_stats.c new file mode 100644 index 000000000000..e609d428811a --- /dev/null +++ b/virt/kvm/binary_stats.c @@ -0,0 +1,146 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * KVM binary statistics interface implementation + * + * Copyright 2021 Google LLC + */ + +#include <linux/kvm_host.h> +#include <linux/kvm.h> +#include <linux/errno.h> +#include <linux/uaccess.h> + +/** + * kvm_stats_read() - 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) +{ + 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 = header->id_offset + KVM_STATS_NAME_SIZE - pos; + copylen = min(copylen, remain); + if (copylen > 0) { + src = id + pos - header->id_offset; + 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; +} |