hwmonio.hpp

#pragma once

#include <chrono>
#include <string>

namespace hwmonio
{

static constexpr auto retries = 10;
static constexpr auto delay = std::chrono::milliseconds{100};

/** @class HwmonIOInterface
 *  @brief Abstract base class defining a HwmonIOInterface.
 *
 *  This is initially to provide easier testing through injection,
 *  however, could in theory support non-sysfs handling of hwmon IO.
 */
class HwmonIOInterface
{
  public:
    virtual ~HwmonIOInterface() = default;

    virtual int64_t read(const std::string& type, const std::string& id,
                         const std::string& sensor, size_t retries,
                         std::chrono::milliseconds delay) const = 0;

    virtual void write(uint32_t val, const std::string& type,
                       const std::string& id, const std::string& sensor,
                       size_t retries,
                       std::chrono::milliseconds delay) const = 0;

    virtual std::string path() const = 0;
};

/** @class HwmonIO
 *  @brief Convenience wrappers for HWMON sysfs attribute IO.
 *
 *  Unburden the rest of the application from having to check
 *  ENOENT after every hwmon attribute io operation.  Hwmon
 *  device drivers can be unbound at any time; the program
 *  cannot always be terminated externally before we try to
 *  do an io.
 */
class HwmonIO : public HwmonIOInterface
{
  public:
    HwmonIO() = delete;
    HwmonIO(const HwmonIO&) = default;
    HwmonIO(HwmonIO&&) = default;
    HwmonIO& operator=(const HwmonIO&) = default;
    HwmonIO& operator=(HwmonIO&&) = default;
    ~HwmonIO() = default;

    /** @brief Constructor
     *
     *  @param[in] path - hwmon instance root - eg:
     *      /sys/class/hwmon/hwmon<N>
     */
    explicit HwmonIO(const std::string& path);

    /** @brief Perform formatted hwmon sysfs read.
     *
     *  Propagates any exceptions other than ENOENT.
     *  ENOENT will result in a call to exit(0) in case
     *  the underlying hwmon driver is unbound and
     *  the program is inadvertently left running.
     *
     *  For possibly transient errors will retry up to
     *  the specified number of times.
     *
     *  @param[in] type - The hwmon type (ex. temp).
     *  @param[in] id - The hwmon id (ex. 1).
     *  @param[in] sensor - The hwmon sensor (ex. input).
     *  @param[in] retries - The number of times to retry.
     *  @param[in] delay - The time to sleep between retry attempts.
     *
     *  @return val - The read value.
     */
    int64_t read(const std::string& type, const std::string& id,
                 const std::string& sensor, size_t retries,
                 std::chrono::milliseconds delay) const override;

    /** @brief Perform formatted hwmon sysfs write.
     *
     *  Propagates any exceptions other than ENOENT.
     *  ENOENT will result in a call to exit(0) in case
     *  the underlying hwmon driver is unbound and
     *  the program is inadvertently left running.
     *
     *  For possibly transient errors will retry up to
     *  the specified number of times.
     *
     *  @param[in] val - The value to be written.
     *  @param[in] type - The hwmon type (ex. fan).
     *  @param[in] id - The hwmon id (ex. 1).
     *  @param[in] retries - The number of times to retry.
     *  @param[in] delay - The time to sleep between retry attempts.
     */
    void write(uint32_t val, const std::string& type, const std::string& id,
               const std::string& sensor, size_t retries,
               std::chrono::milliseconds delay) const override;

    /** @brief Hwmon instance path access.
     *
     *  @return path - The hwmon instance path.
     */
    std::string path() const override;

  private:
    std::string _p;
};
} // namespace hwmonio

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