compression-algorithm=algo(param,param) recompalgo(param,param) (glob…

…al,recomp,params)

Ref: systemd#178 (comment)

man/zram-generator.conf.md

@@ -72,10 +72,14 @@ Devices with the final size of *0* will be discarded.
 
   Specifies the algorithm used to compress the zram device.
 
-  This takes a literal string, representing the algorithm to use.<br />
-  Consult */sys/block/zram0/comp_algorithm* for a list of currently loaded compression algorithms, but note that additional ones may be loaded on demand.
+  This takes a whitespace-separated list string, representing the algorithms to use, and parameters in parenteses.<br />
+  Consult */sys/block/zram0/comp_algorithm* (and *.../recomp_algorithm*) for a list of currently loaded compression algorithms, but note that additional ones may be loaded on demand.
 
-  If unset, none will be configured and the kernel's default will be used.
+  If unset, none will be configured and the kernel's default will be used.<br />
+  If more than one is given, and recompression is enabled in the kernel, subsequent ones will be set as the recompression algorithms, with decreasing priority.
+
+  If a compression algorithm is suffixed with a parenthesised comma-separated list of parameters, those are given to `.../algorithm_params` (and `.../recompress`).
+  A parenthesised parameter list *without* a compression algorithm is set as the global recompression parameters.
 
 * `writeback-device`=
 

src/config.rs

@@ -22,7 +22,7 @@ pub struct Device {
 
     /// Default: `DEFAULT_ZRAM_SIZE`
     pub zram_size: Option<(String, fasteval::ExpressionI, fasteval::Slab)>,
-    pub compression_algorithm: Option<String>,
+    pub compression_algorithms: Algorithms,
     pub writeback_dev: Option<PathBuf>,
     pub disksize: u64,
 
@@ -50,7 +50,7 @@ impl Device {
             name,
             host_memory_limit_mb: None,
             zram_size: None,
-            compression_algorithm: None,
+            compression_algorithms: Default::default(),
             writeback_dev: None,
             disksize: 0,
             zram_resident_limit: None,
@@ -165,7 +165,7 @@ impl fmt::Display for Device {
                 .as_ref()
                 .map(|zs| &zs.0[..])
                 .unwrap_or(DEFAULT_RESIDENT_LIMIT),
-            self.compression_algorithm.as_deref().unwrap_or("<default>"),
+            self.compression_algorithms,
             self.writeback_dev.as_deref().unwrap_or_else(|| Path::new("<none>")).display(),
             self.options
         )?;
@@ -196,6 +196,35 @@ impl fmt::Display for OptMB {
     }
 }
 
+#[derive(Default, Debug, PartialEq, Eq)]
+pub struct Algorithms {
+    pub compression_algorithms: Vec<(String, String)>,  // algorithm, params; first one is real compression, later ones are recompression
+    pub recompression_global: String, // params
+}
+impl fmt::Display for Algorithms {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match &self.compression_algorithms[..] {
+            [] => f.write_str("<default>")?,
+            [(first, firstparams), more @ ..] => {
+                f.write_str(first)?;
+                if !firstparams.is_empty() {
+                    write!(f, " ({})", firstparams)?;
+                }
+                for (algo, params) in more {
+                    write!(f, " then {}", algo)?;
+                    if !params.is_empty() {
+                        write!(f, " ({})", params)?;
+                    }
+                }
+            }
+        }
+        if !self.recompression_global.is_empty() {
+            write!(f, "(global recompress: {})", self.recompression_global)?;
+        }
+        Ok(())
+    }
+}
+
 struct RamNs(f64);
 impl fasteval::EvalNamespace for RamNs {
     fn lookup(&mut self, name: &str, args: Vec<f64>, _: &mut String) -> Option<f64> {
@@ -360,6 +389,21 @@ fn parse_size_expr(
     ))
 }
 
+fn parse_compression_algorithm_params(whole: &str) -> (String, String) {
+    if let Some(paren) = whole.find('(')  {
+        let (algo, mut params) = whole.split_at(paren);
+        dbg!((algo, params));
+        params = &params[1..];
+        if params.ends_with(')') {
+            params = &params[..params.len() - 1];
+        }
+        dbg!((algo, params));
+        return (algo.to_string(), params.replace(',', " "));
+    } else {
+        return (whole.to_string(), String::new());
+    }
+}
+
 fn parse_line(dev: &mut Device, key: &str, value: &str) -> Result<()> {
     match key {
         "host-memory-limit" | "memory-limit" => {
@@ -376,7 +420,16 @@ fn parse_line(dev: &mut Device, key: &str, value: &str) -> Result<()> {
         }
 
         "compression-algorithm" => {
-            dev.compression_algorithm = Some(value.to_string());
+            dev.compression_algorithms = value.split_whitespace().fold(Default::default(), |mut algos, s| {
+                let (algo, params) = parse_compression_algorithm_params(s);
+                dbg!((&algo, &params));
+                if algo.is_empty() {
+                    algos.recompression_global = params;
+                } else {
+                    algos.compression_algorithms.push((algo, params));
+                }
+                algos
+            });
         }
 
         "writeback-device" => {

src/generator.rs

@@ -117,7 +117,7 @@ pub fn run_generator(devices: &[Device], output_directory: &Path, fake_mode: boo
 
     let compressors: BTreeSet<_> = devices
         .iter()
-        .flat_map(|device| device.compression_algorithm.as_deref())
+        .flat_map(|device| device.compression_algorithms.compression_algorithms.iter().map(|(a, _)| a.as_ref()))
         .collect();
 
     if !compressors.is_empty() {

src/setup.rs

@@ -24,20 +24,49 @@ pub fn run_device_setup(device: Option<Device>, device_name: &str) -> Result<()>
 
     let device_sysfs_path = Path::new("/sys/block").join(device_name);
 
-    if let Some(ref compression_algorithm) = device.compression_algorithm {
-        let comp_algorithm_path = device_sysfs_path.join("comp_algorithm");
-        match fs::write(&comp_algorithm_path, compression_algorithm) {
-            Ok(_) => {}
+    for (prio, (algo, params)) in device.compression_algorithms.compression_algorithms.iter().enumerate() {
+        let params = if params.is_empty() { None } else { Some(params) };
+        let (path, data, add_pathdata) = if prio == 0 {
+            (device_sysfs_path.join("comp_algorithm"), algo,
+                params.as_ref().map(|p| (device_sysfs_path.join("algorithm_params"), format!("algo={} {}", algo, p))))
+        } else {
+            (
+                device_sysfs_path.join("recomp_algorithm"),
+                &format!("algo={} priority={}", algo, prio),
+                params.as_ref().map(|p| (device_sysfs_path.join("recompress"), format!("{} priority={}", p, prio))),
+            )
+        };
+
+        match fs::write(&path, data) {
+            Ok(_) => {
+                if let Some((add_path, add_data)) = add_pathdata {
+                    match fs::write(add_path, add_data) {
+                        Ok(_) => {}
+                        Err(err) => {
+                            warn!(
+                                "Warning: algorithm {:?} supplemental data {:?} not written: {}",
+                                algo, data, err,
+                            );
+                        }
+                    }
+                }
+            }
             Err(err) if err.kind() == ErrorKind::InvalidInput => {
                 warn!(
                     "Warning: algorithm {:?} not recognised; consult {} for a list of available ones",
-                    compression_algorithm, comp_algorithm_path.display(),
+                    algo, path.display(),
+                );
+            }
+            Err(err) if err.kind() == ErrorKind::PermissionDenied && prio != 0 => {
+                warn!(
+                    "Warning: recompression algorithm {:?} requested but recompression not available ({} doesn't exist)",
+                    algo, path.display(),
                 );
             }
             err @ Err(_) => err.with_context(|| {
                 format!(
                     "Failed to configure compression algorithm into {}",
-                    comp_algorithm_path.display()
+                    path.display()
                 )
             })?,
         }

tests/09-zram-size/etc/systemd/zram-generator.conf

@@ -1,4 +1,4 @@
 [zram0]
-compression-algorithm = zstd
+compression-algorithm = zstd(dictionary=/etc/gaming,level=9) (recompargs)
 host-memory-limit = 2050
 zram-size = min(0.75 * ram, 6000)

tests/test_cases.rs

@@ -124,7 +124,7 @@ fn test_02_zstd() {
     assert!(d.is_swap());
     assert_eq!(d.host_memory_limit_mb, Some(2050));
     assert_eq!(d.zram_size.as_ref().map(z_s_name), Some("ram * 0.75"));
-    assert_eq!(d.compression_algorithm.as_ref().unwrap(), "zstd");
+    assert_eq!(d.compression_algorithms, config::Algorithms { compression_algorithms: vec![("zstd".into(), "".into())], ..Default::default() });
     assert_eq!(d.options, "discard");
 }
 
@@ -259,7 +259,7 @@ fn test_09_zram_size() {
         d.zram_size.as_ref().map(z_s_name),
         Some("min(0.75 * ram, 6000)")
     );
-    assert_eq!(d.compression_algorithm.as_ref().unwrap(), "zstd");
+    assert_eq!(d.compression_algorithms, config::Algorithms { compression_algorithms: vec![("zstd".into(), "dictionary=/etc/gaming level=9".into())], recompression_global: "recompargs".into() });
 }
 
 #[test]
@@ -283,7 +283,7 @@ fn test_10_example() {
                     d.zram_size.as_ref().map(z_s_name),
                     Some("min(ram / 10, 2048)")
                 );
-                assert_eq!(d.compression_algorithm.as_deref(), Some("lzo-rle"));
+                assert_eq!(d.compression_algorithms, config::Algorithms { compression_algorithms: vec![("lzo-rle".into(), "".into()), ("zstd".into(), "level=3".into())], ..Default::default() });
                 assert_eq!(d.options, "");
             }
             "zram1" => {

zram-generator.conf.example

@@ -29,7 +29,13 @@ zram-resident-limit = 0
 
 # The compression algorithm to use for the zram device,
 # or leave unspecified to keep the kernel default.
-compression-algorithm = lzo-rle
+#
+# Subsequent algorithms are used for recompression.
+# Comma-separated parameters may be specified in parentheses.
+#
+# Parameters without a compression algorithm are set as
+# global recompression parameters.
+compression-algorithm = lzo-rle zstd(level=3) (type=idle)
 
 # By default, file systems and swap areas are trimmed on-the-go
 # by setting "discard".