diff --git a/Cargo.toml b/Cargo.toml
index 35bf9b9..92256fe 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,3 +6,7 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+
+[features]
+default = []
+derive = []
diff --git a/src/attribute.rs b/src/attribute.rs
index 405049e..a1967db 100644
--- a/src/attribute.rs
+++ b/src/attribute.rs
@@ -5,7 +5,7 @@ use std::str::FromStr;
 use crate::EitherErr2;
 
 /// sysfs entity attribute file functionality
-pub trait SysAttribute: Eq {
+pub trait SysAttribute {
     /// attribute file name
     fn filename(&self) -> PathBuf;
     
@@ -29,6 +29,11 @@ pub trait SysAttribute: Eq {
     fn write_value(&self, entity: &dyn crate::SysEntity, value: &[u8]) -> IoResult<()> {
         std::fs::write(self.path(entity), value)
     }
+
+    /// Returns true if the attribute is readonly
+    fn readonly(&self, entity: &dyn crate::SysEntity) -> bool {
+        self.path(entity).metadata().map(|meta| meta.permissions().readonly()).unwrap_or(false)
+    }
 }
 
 impl SysAttribute for String {
@@ -37,8 +42,14 @@ impl SysAttribute for String {
     }
 }
 
+impl SysAttribute for &str {
+    fn filename(&self) -> PathBuf {
+        PathBuf::from(self)
+    }
+}
+
 /// sysfs entity attribute functionality extension
-pub trait SysAttributeExt: SysAttribute {
+pub trait SysAttributeExt: SysAttribute + Eq {
     /// read attribute as string
     fn read_str(&self, entity: &dyn crate::SysEntity) -> IoResult<String> {
         std::fs::read_to_string(self.path(entity))
@@ -56,4 +67,4 @@ pub trait SysAttributeExt: SysAttribute {
     }
 }
 
-impl <X: SysAttribute> SysAttributeExt for X {}
+impl <X: SysAttribute + Eq> SysAttributeExt for X {}
diff --git a/src/basic.rs b/src/basic.rs
index 375c095..2174f51 100644
--- a/src/basic.rs
+++ b/src/basic.rs
@@ -5,6 +5,7 @@ use std::io::Result as IoResult;
 const SYS_CLASS_PATH: &str = "sys/class";
 
 /// Generic entity path with basic functionality
+#[cfg_attr(feature = "derive", derive(Debug, Clone))]
 pub struct BasicEntityPath {
     path: PathBuf
 }
@@ -61,7 +62,7 @@ impl crate::SysEntity for BasicEntityPath {
     }
 }
 
-impl crate::SysEntityAttributes<String, String, <String as std::str::FromStr>::Err> for BasicEntityPath {
+impl crate::SysEntityAttributes<String> for BasicEntityPath {
     fn capabilities(&self) -> Vec<String> {
         if let Ok(dir_iter) = self.path.read_dir() {
             dir_iter.filter_map(
diff --git a/src/capability.rs b/src/capability.rs
new file mode 100644
index 0000000..4dc74d1
--- /dev/null
+++ b/src/capability.rs
@@ -0,0 +1,53 @@
+//! sysfs class entity capability filtering
+
+/// Capabilities filter
+pub trait Capabilities<A: crate::SysAttribute, R: std::borrow::Borrow<A>> {
+    /// Are the required capabilities (self) satisfied by the provided capabilities (the parameter)?
+    fn can(&mut self, capabilities: &Vec<R>) -> bool;
+}
+
+impl <F: FnMut(&Vec<R>) -> bool, A: crate::SysAttribute, R: std::borrow::Borrow<A>> Capabilities<A, R> for F {
+    fn can(&mut self, capabilities: &Vec<R>) -> bool {
+        (self)(capabilities)
+    }
+}
+
+/// Build a Capabilities implementor which needs specific attributes to exist
+pub fn attributes<'a, A: crate::SysAttribute + Eq + 'a, R: std::borrow::Borrow<A> + 'a>(attributes: impl Iterator<Item=R>) -> impl Capabilities<A, R> + 'a {
+    AllNeedsCapabilities::new(
+        attributes.map(|attr: R| { move |other_attr: &R| attr.borrow() == other_attr.borrow() }).collect()
+    )
+}
+
+
+struct AllNeedsCapabilities<'a, 'f, A: crate::SysAttribute + 'a, R: std::borrow::Borrow<A> + 'a, F: (FnMut(&R) -> bool) + 'f> {
+    wanted: Vec<F>,
+    _attr_ty: std::marker::PhantomData<A>,
+    _attr_brw_ty: std::marker::PhantomData<R>,
+    _life_attr_ty: std::marker::PhantomData<&'a ()>,
+    _life_fn_ty: std::marker::PhantomData<&'f ()>,
+}
+
+impl <'a, 'f, A: crate::SysAttribute + 'a, R: std::borrow::Borrow<A> + 'a, F: (FnMut(&R) -> bool) + 'f> AllNeedsCapabilities<'a, 'f, A, R, F> {
+    pub(crate) fn new(wanted: Vec<F>) -> Self {
+        Self {
+            wanted,
+            _attr_ty: Default::default(),
+            _attr_brw_ty: Default::default(),
+            _life_attr_ty: Default::default(),
+            _life_fn_ty: Default::default(),
+        }
+    }
+}
+
+impl <'a, 'f, A: crate::SysAttribute + 'a, R: std::borrow::Borrow<A> + 'a, F: (FnMut(&R) -> bool) + 'f> Capabilities<A, R> for AllNeedsCapabilities<'a, 'f, A, R, F> {
+    fn can(&mut self, capabilities: &Vec<R>) -> bool {
+        let mut wants = vec![false; self.wanted.len()];
+        for capability in capabilities {
+            if let Some(pos) = self.wanted.iter_mut().position(|w| w(capability)) {
+                wants[pos] = true;
+            }
+        }
+        wants.into_iter().all(|item| item)
+    }
+}
diff --git a/src/entity.rs b/src/entity.rs
index ee21e9c..40f3041 100644
--- a/src/entity.rs
+++ b/src/entity.rs
@@ -6,18 +6,39 @@ use crate::EitherErr2;
 use crate::SysAttributeExt;
 
 /// sysfs class entity functionality
-pub trait SysEntity: AsRef<Path> {
+#[cfg(feature = "derive")]
+pub trait SysEntity: AsRef<Path> + core::fmt::Debug {
     /// Convert specialized entity into general entity path container
     fn to_entity_path(self) -> EntityPath;
     
     /// Get the entity's name
     fn name(&self) -> IoResult<String>;
+
+    /// Try to get the entity's root sysfs dir (probably `/`)
+    fn root(&self) -> Option<crate::SysPath> {
+        crate::SysPath::from_entity_path(self)
+    }
+}
+
+/// sysfs class entity functionality
+#[cfg(not(feature = "derive"))]
+pub trait SysEntity: AsRef<Path> {
+    /// Convert specialized entity into general entity path container
+    fn to_entity_path(self) -> EntityPath;
+
+    /// Get the entity's name
+    fn name(&self) -> IoResult<String>;
+
+    /// Try to get the entity's root sysfs dir (probably `/`)
+    fn root(&self) -> Option<crate::SysPath> {
+        crate::SysPath::from_entity_path(self)
+    }
 }
 
 /// sysfs class entity functionality extension
 pub trait SysEntityRawExt: SysEntity {
     /// Get an attribute on the entity
-    fn attribute<A: crate::SysAttribute, T: std::str::FromStr<Err=E>, E>(&self, attr: A) -> Result<T, EitherErr2<std::io::Error, E>>;
+    fn attribute<A: crate::SysAttribute + Eq, T: std::str::FromStr<Err=E>, E>(&self, attr: A) -> Result<T, EitherErr2<std::io::Error, E>>;
     /// Get an attribute by filename in the entity's directory
     fn attribute_str<A: AsRef<Path>>(&self, attr: A) -> IoResult<String>;
     
@@ -29,7 +50,7 @@ pub trait SysEntityRawExt: SysEntity {
 }
 
 impl <X: SysEntity> SysEntityRawExt for X {
-    fn attribute<A: crate::SysAttribute, T: std::str::FromStr<Err=E>, E>(&self, attr: A) -> Result<T, EitherErr2<std::io::Error, E>> {
+    fn attribute<A: crate::SysAttribute + Eq, T: std::str::FromStr<Err=E>, E>(&self, attr: A) -> Result<T, EitherErr2<std::io::Error, E>> {
         attr.parse(self)
     }
     
@@ -48,21 +69,26 @@ impl <X: SysEntity> SysEntityRawExt for X {
 
 
 /// sysfs class entity attribute type indicator
-pub trait SysEntityAttributes<A: crate::SysAttribute, T: std::str::FromStr<Err=E>, E>: SysEntity + Sized {
-    /// Get an attribute on the entity
-    fn attribute(&self, attr: A) -> Result<T, EitherErr2<std::io::Error, E>> {
-        attr.parse(self)
-    }
-    
+pub trait SysEntityAttributes<A: crate::SysAttribute + Eq>: SysEntity + Sized {
     /// Get attributes available on this entity;
     fn capabilities(&self) -> Vec<A>;
 }
 
-/*pub trait SysEntityAttributesExt<A: crate::SysAttribute, T: std::str::FromStr<Err=E>, E>: SysEntityAttributes<A, T, E> {
-    fn attribute()
-}*/
+pub trait SysEntityAttributesExt<A: crate::SysAttribute + Eq>: SysEntityAttributes<A> {
+    fn capable<C: crate::capability::Capabilities<A, A>>(&self, mut capabilities: C) -> bool {
+        capabilities.can(&self.capabilities())
+    }
+
+    /// Get an attribute on the entity
+    fn attribute<T: std::str::FromStr<Err=E>, E>(&self, attr: A) -> Result<T, EitherErr2<std::io::Error, E>> {
+        attr.parse(self)
+    }
+}
+
+impl <A: crate::SysAttribute + Eq, X: SysEntityAttributes<A>> SysEntityAttributesExt<A> for X {}
 
 /// sysfs class entity implementors
+#[cfg_attr(feature = "derive", derive(Debug, Clone))]
 pub enum EntityPath {
     /// hwmon
     HwMon(crate::HwMonPath),
@@ -71,7 +97,7 @@ pub enum EntityPath {
     /// Generic
     Generic(crate::BasicEntityPath),
     /// Miscellaneous
-    Custom(Box<dyn SysEntity>),
+    Custom(std::sync::Arc<Box<dyn SysEntity>>),
 }
 
 impl EntityPath {
@@ -80,19 +106,14 @@ impl EntityPath {
             Self::HwMon(inner) => inner,
             Self::PowerSupply(inner) => inner,
             Self::Generic(inner) => inner,
-            Self::Custom(inner) => inner.as_ref(),
+            Self::Custom(inner) => inner.as_ref().as_ref(),
         }
     }
 }
 
 impl AsRef<Path> for EntityPath {
     fn as_ref(&self) -> &Path {
-        match self {
-            Self::HwMon(inner) => inner.as_ref(),
-            Self::PowerSupply(inner) => inner.as_ref(),
-            Self::Generic(inner) => inner.as_ref(),
-            Self::Custom(inner) => inner.as_ref().as_ref(),
-        }
+        self.inner().as_ref()
     }
 }
 
diff --git a/src/errors.rs b/src/errors.rs
index cb2265b..b641af2 100644
--- a/src/errors.rs
+++ b/src/errors.rs
@@ -1,5 +1,5 @@
 /// Multi-error convenience enum
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum EitherErr2<T1, T2> {
     /// Type 1
     First(T1),
@@ -32,7 +32,7 @@ impl <T1: std::error::Error, T2: std::error::Error> std::error::Error for Either
 
 /// Value parse error for an enumeration.
 /// This usually indicates an unexpected value (one without an enum variant) was received while parsing.
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct ValueEnumError<'a> {
     pub(crate) got: String,
     pub(crate) allowed: &'a [&'a str],
diff --git a/src/hwmon.rs b/src/hwmon.rs
index a0911c8..faed7a2 100644
--- a/src/hwmon.rs
+++ b/src/hwmon.rs
@@ -7,11 +7,13 @@ const HWMON_DIR_PATH: &'static str = "sys/class/hwmon/";
 /// Attribute representation.
 /// Attribute files are usually in the format `<type><number>_<item>`.
 #[derive(Clone, Copy, PartialEq, Eq)]
+#[cfg_attr(feature = "derive", derive(Debug))]
 pub struct HwMonAttribute {
    inner: HwMonAttributeInner,
 }
 
 #[derive(Clone, Copy, PartialEq, Eq)]
+#[cfg_attr(feature = "derive", derive(Debug))]
 enum HwMonAttributeInner {
     Name,
     Standard {
@@ -20,6 +22,7 @@ enum HwMonAttributeInner {
         item: HwMonAttributeItem,
     },
     Uevent,
+    Custom(&'static str),
 }
 
 impl std::str::FromStr for HwMonAttributeInner {
@@ -46,6 +49,7 @@ impl std::str::FromStr for HwMonAttributeInner {
 
 /// Attribute type in the format `<type><number>_<item>`
 #[derive(Clone, Copy, PartialEq, Eq)]
+#[cfg_attr(feature = "derive", derive(Debug))]
 pub enum HwMonAttributeType {
     /// Voltage
     In,
@@ -84,6 +88,7 @@ impl HwMonAttributeType {
 
 /// Attribute item in the format `<type><number>_<item>`
 #[derive(Clone, Copy, PartialEq, Eq)]
+#[cfg_attr(feature = "derive", derive(Debug))]
 pub enum HwMonAttributeItem {
     /// Input
     Input,
@@ -136,12 +141,20 @@ impl HwMonAttribute {
             inner: HwMonAttributeInner::Uevent
         }
     }
+
+    /// Custom entity attribute
+    pub const fn custom(attr: &'static str) -> Self {
+        Self {
+            inner: HwMonAttributeInner::Custom(attr)
+        }
+    }
     
     fn to_attr_str(&self) -> String {
         match self.inner {
             HwMonAttributeInner::Name => "name".to_string(),
             HwMonAttributeInner::Standard { ty, number, item } => format!("{}{}_{}", ty.to_attr_str(), number, item.to_attr_str()),
             HwMonAttributeInner::Uevent => "uevent".to_string(),
+            HwMonAttributeInner::Custom(s) => s.to_owned(),
         }
     }
 }
@@ -153,6 +166,7 @@ impl crate::SysAttribute for HwMonAttribute {
 }
 
 /// hwmon<number>/ directory
+#[cfg_attr(feature = "derive", derive(Debug, Clone))]
 pub struct HwMonPath {
     path: PathBuf
 }
@@ -226,7 +240,7 @@ impl crate::SysEntity for HwMonPath {
     }
 }
 
-impl crate::SysEntityAttributes<HwMonAttribute, String, <String as std::str::FromStr>::Err> for HwMonPath {
+impl crate::SysEntityAttributes<HwMonAttribute> for HwMonPath {
     fn capabilities(&self) -> Vec<HwMonAttribute> {
         if let Ok(dir_iter) = self.path.read_dir() {
             dir_iter.filter_map(
diff --git a/src/lib.rs b/src/lib.rs
index 1acc06a..8384d6f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -10,6 +10,8 @@ pub use attribute::{SysAttribute, SysAttributeExt};
 mod basic;
 pub use basic::BasicEntityPath;
 
+pub mod capability;
+
 mod entity;
 pub use entity::{EntityPath, SysEntity, SysEntityRawExt, SysEntityAttributes};
 
diff --git a/src/power_supply.rs b/src/power_supply.rs
index 86a3ff2..6e39cb1 100644
--- a/src/power_supply.rs
+++ b/src/power_supply.rs
@@ -11,7 +11,8 @@ const CLASS_PATH: &'static str = "power_supply";
 
 /// Attribute files in a power supply directory
 /// These attributes are taken from https://github.com/torvalds/linux/blob/master/Documentation/ABI/testing/sysfs-class-power
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Clone, Copy, PartialEq, Eq)]
+#[cfg_attr(feature = "derive", derive(Debug))]
 pub enum PowerSupplyAttribute {
     /// Reports the name of the device manufacturer.
     Manufacturer,
@@ -65,6 +66,12 @@ pub enum PowerSupplyAttribute {
     ChargeType,
     /// Reports the charging current value which is used to determine when the battery is considered full and charging should end (uA).
     ChargeTermCurrent,
+    /// Reports the instantaneous charge value of the power supply (uA).
+    ChargeNow,
+    /// Reports the maximum charge value of the power supply (uA).
+    ChargeFull,
+    /// Reports the maximum rated charge value of the power supply (uA).
+    ChargeFullDesign,
     /// Reports the health of the battery or battery side of charger functionality ( "Unknown", "Good", "Overheat", "Dead", "Over voltage", "Unspecified failure", "Cold", "Watchdog timer expire", "Safety timer expire", "Over current", "Calibration required", "Warm", "Cool", "Hot", or "No battery").
     Health,
     /// Reports the charging current applied during pre-charging phase for a battery charge cycle (uA).
@@ -82,6 +89,8 @@ pub enum PowerSupplyAttribute {
     /// Reports the number of full charge + discharge cycles the battery has undergone.
     CycleCount,
     // TODO USB properties
+    /// Custom entity attribute
+    Custom(&'static str)
 }
 
 impl crate::SysAttribute for PowerSupplyAttribute {
@@ -113,6 +122,9 @@ impl crate::SysAttribute for PowerSupplyAttribute {
             Self::ChargeControlEndThreshold => "charge_control_end_threshold",
             Self::ChargeType => "charge_type",
             Self::ChargeTermCurrent => "charge_term_current",
+            Self::ChargeNow => "charge_now",
+            Self::ChargeFull => "charge_full",
+            Self::ChargeFullDesign => "charge_full_design",
             Self::Health => "health",
             Self::PrechargeCurrent => "precharge_current",
             Self::Present => "present",
@@ -121,13 +133,15 @@ impl crate::SysAttribute for PowerSupplyAttribute {
             Self::Technology => "technology",
             Self::VoltageAverage => "voltage_avg",
             Self::CycleCount => "cycle_count",
+            Self::Custom(s) => s,
         };
         s.into()
     }
 }
 
 /// power_supply/<entity>/type attribute value
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Clone, Copy, PartialEq, Eq)]
+#[cfg_attr(feature = "derive", derive(Debug))]
 pub enum PowerSupplyType {
     /// Battery
     Battery,
@@ -184,6 +198,7 @@ impl std::str::FromStr for PowerSupplyType {
 }
 
 /// power_supply/<entity>/ directory
+#[cfg_attr(feature = "derive", derive(Debug, Clone))]
 pub struct PowerSupplyPath {
     inner: crate::BasicEntityPath,
 }
@@ -229,7 +244,7 @@ impl crate::SysEntity for PowerSupplyPath {
     }
 }
 
-impl crate::SysEntityAttributes<PowerSupplyAttribute, String, <String as std::str::FromStr>::Err> for PowerSupplyPath {
+impl crate::SysEntityAttributes<PowerSupplyAttribute> for PowerSupplyPath {
     fn capabilities(&self) -> Vec<PowerSupplyAttribute> {
         self.inner.filter_capabilities(vec![
             PowerSupplyAttribute::Manufacturer,
@@ -278,6 +293,10 @@ mod tests {
     
     #[test]
     fn power_supply_all() -> std::io::Result<()> {
+        if std::fs::read_dir("/sys/class/power_supply")?.count() == 0 {
+            eprintln!("power_supply test skipped since none exist (maybe running on a desktop PC?)");
+            return Ok(())
+        }
         let sys = crate::SysPath::default();
         let all_psu: Vec<_> = PowerSupplyPath::all(sys)?.collect();
         assert!(!all_psu.is_empty());
diff --git a/src/syspath.rs b/src/syspath.rs
index c0dd0e9..b069dae 100644
--- a/src/syspath.rs
+++ b/src/syspath.rs
@@ -1,9 +1,10 @@
 use std::path::{Path, PathBuf};
 use std::convert::AsRef;
 
-use crate::SysEntity;
+use crate::{SysEntity, SysEntityAttributes};
 
 /// sysfs root
+#[cfg_attr(feature = "derive", derive(Debug))]
 pub struct SysPath {
     root: PathBuf,
 }
@@ -35,16 +36,42 @@ impl SysPath {
     }
     
     /// Find a hardware monitor entry by index
-    pub fn hwmon_by_index(&self, index: u64) -> std::io::Result<crate::HwMonPath> {
+    pub fn hwmon_by_index(&self, index: u64) -> crate::HwMonPath {
         let entry = crate::HwMonPath::entry(self, index);
-        entry.attribute(crate::HwMonAttribute::name())?;
-        Ok(entry)
+        //entry.attribute(crate::HwMonAttribute::name())?;
+        entry
+    }
+
+    /// Find a hardware monitor by capabilities
+    pub fn hwmon(&self, mut c: impl crate::capability::Capabilities<crate::HwMonAttribute, crate::HwMonAttribute>) -> std::io::Result<impl Iterator<Item=crate::HwMonPath>> {
+        Ok(crate::HwMonPath::all(self.root.clone())?
+            .filter_map(|p| p.ok())
+            .filter(move |p| c.can(&p.capabilities())))
     }
     
     /// Find a power supply entry by name
-    pub fn power_supply(&self, name: &str) -> crate::PowerSupplyPath {
+    pub fn power_supply_by_name(&self, name: &str) -> crate::PowerSupplyPath {
         crate::PowerSupplyPath::name(self, name)
     }
+
+    /// Find a power supply by capabilities
+    pub fn power_supply(&self, mut c: impl crate::capability::Capabilities<crate::PowerSupplyAttribute, crate::PowerSupplyAttribute>) -> std::io::Result<impl Iterator<Item=crate::PowerSupplyPath>> {
+        Ok(crate::PowerSupplyPath::all(self.root.clone())?
+            .filter_map(|p| p.ok())
+            .filter(move |p| c.can(&p.capabilities())))
+    }
+
+    /// Find entities in a sysfs class by capabilities
+    pub fn class(&self, class: impl AsRef<Path>, mut c: impl crate::capability::Capabilities<String, String>) -> std::io::Result<impl Iterator<Item=crate::BasicEntityPath>> {
+        Ok(crate::BasicEntityPath::all(self.root.clone(), class)?
+            .filter_map(|p| p.ok())
+            .filter(move |p| c.can(&p.capabilities()))
+        )
+    }
+
+    pub(crate) fn from_entity_path(entity: impl AsRef<Path>) -> Option<Self> {
+        Some(Self::path(entity.as_ref().parent()?.parent()?.parent()?.parent()?))
+    }
 }
 
 impl std::default::Default for SysPath {
@@ -60,3 +87,23 @@ impl AsRef<Path> for SysPath {
         self.root.as_path()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::SysEntity;
+
+    #[test]
+    fn syspath_root_recovery() -> std::io::Result<()> {
+        let sys = crate::SysPath::default();
+        let all_ent: Vec<_> = crate::BasicEntityPath::all(&sys, "hwmon")?.collect();
+        assert!(!all_ent.is_empty());
+        for p in all_ent.into_iter() {
+            let p = p?;
+            let root_opt = p.root();
+            assert!(root_opt.is_some());
+            assert_eq!(sys.as_ref(), root_opt.unwrap().as_ref());
+        }
+        Ok(())
+    }
+}