ext2: Support customized parameters

Allow changing {blocks,inodes}_per_group.

BUG=b:329359333
TEST=cargo test

Change-Id: I1646f80dbe92dbdafbe4147a8abbd141784aff69
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/5400932
Commit-Queue: Keiichi Watanabe <keiichiw@chromium.org>
Reviewed-by: Takaya Saeki <takayas@chromium.org>

5 files changed, 52 insertions, 13 deletions

diff --git a/ext2/examples/mkfs.rs b/ext2/examples/mkfs.rs
index 91e5ed6a1..d602fe6a9 100644
--- a/ext2/examples/mkfs.rs
+++ b/ext2/examples/mkfs.rs
@@ -15,16 +15,27 @@ mod linux {
 
     #[derive(FromArgs)]
     /// Create ext2 filesystem.
-    struct Config {
+    struct Args {
         /// path to the disk,
         #[argh(option)]
         path: String,
+
+        /// number of blocks for each group
+        #[argh(option, default = "1024")]
+        blocks_per_group: u32,
+
+        /// number of inodes for each group
+        #[argh(option, default = "1024")]
+        inodes_per_group: u32,
     }
 
     pub fn main() -> anyhow::Result<()> {
-        let cfg: Config = argh::from_env();
-        let ext2 = Ext2::new()?;
-        println!("Create {}", cfg.path);
+        let args: Args = argh::from_env();
+        let ext2 = Ext2::new(&ext2::Config {
+            blocks_per_group: args.blocks_per_group,
+            inodes_per_group: args.inodes_per_group,
+        })?;
+        println!("Create {}", args.path);
         let mem = ext2.write_to_memory()?;
         // SAFETY: `mem` has a valid pointer and its size.
         let buf = unsafe { std::slice::from_raw_parts(mem.as_ptr(), mem.size()) };
@@ -32,8 +43,9 @@ mod linux {
             .write(true)
             .create(true)
             .truncate(true)
-            .open(&cfg.path)
+            .open(&args.path)
             .unwrap();
+
         file.write_all(buf).unwrap();
 
         Ok(())
diff --git a/ext2/src/fs.rs b/ext2/src/fs.rs
index e98a2f840..bd8e0e803 100644
--- a/ext2/src/fs.rs
+++ b/ext2/src/fs.rs
@@ -11,6 +11,7 @@ use base::MemoryMapping;
 use base::MemoryMappingBuilder;
 use zerocopy::AsBytes;
 
+use crate::superblock::Config;
 use crate::superblock::SuperBlock;
 
 /// A struct to represent an ext2 filesystem.
@@ -20,8 +21,9 @@ pub struct Ext2 {
 
 impl Ext2 {
     /// Create a new ext2 filesystem.
-    pub fn new() -> Result<Self> {
-        let sb = SuperBlock::new()?;
+
+    pub fn new(cfg: &Config) -> Result<Self> {
+        let sb = SuperBlock::new(cfg)?;
         Ok(Ext2 { sb })
     }
 
diff --git a/ext2/src/lib.rs b/ext2/src/lib.rs
index b88a1f17a..85a536e5b 100644
--- a/ext2/src/lib.rs
+++ b/ext2/src/lib.rs
@@ -11,3 +11,4 @@ mod fs;
 mod superblock;
 
 pub use fs::Ext2;
+pub use superblock::Config;
diff --git a/ext2/src/superblock.rs b/ext2/src/superblock.rs
index ca2eb872c..c5bd6e7ea 100644
--- a/ext2/src/superblock.rs
+++ b/ext2/src/superblock.rs
@@ -9,6 +9,14 @@ use zerocopy::AsBytes;
 use zerocopy_derive::FromBytes;
 use zerocopy_derive::FromZeroes;
 
+/// A struct to represent the configuration of an ext2 filesystem.
+pub struct Config {
+    /// The number of blocks per group.
+    pub blocks_per_group: u32,
+    /// The number of inodes per group.
+    pub inodes_per_group: u32,
+}
+
 /// The ext2 superblock.
 ///
 /// The field names are based on [the specification](https://www.nongnu.org/ext2-doc/ext2.html#superblock).
@@ -53,13 +61,13 @@ pub(crate) struct SuperBlock {
 }
 
 impl SuperBlock {
-    pub fn new() -> Result<Self> {
+    pub fn new(cfg: &Config) -> Result<Self> {
         const EXT2_MAGIC_NUMBER: u16 = 0xEF53;
 
         // TODO(b/329359333): Support more than 1 groups for larger data.
         let block_group_nr = 1u16;
-        let blocks_per_group = 1024;
-        let inodes_per_group = 1024;
+        let blocks_per_group = cfg.blocks_per_group;
+        let inodes_per_group = cfg.inodes_per_group;
 
         let log_block_size = 2; // (1024 << log_block_size) = 4K bytes
 
diff --git a/ext2/tests/tests.rs b/ext2/tests/tests.rs
index 963ea8512..3ab9fdc89 100644
--- a/ext2/tests/tests.rs
+++ b/ext2/tests/tests.rs
@@ -10,6 +10,7 @@ use std::path::PathBuf;
 use std::process::Command;
 
 use base::MappedRegion;
+use ext2::Config;
 use ext2::Ext2;
 use tempfile::tempdir;
 
@@ -44,11 +45,10 @@ fn do_autofix(path: &PathBuf, fix_count: usize) {
     println!("output={:?}", output);
 }
 
-#[test]
-fn mkfs_empty() {
+fn mkfs_empty(cfg: &Config) {
     let td = tempdir().unwrap();
     let path = td.path().join("empty.ext2");
-    let ext2 = Ext2::new().unwrap();
+    let ext2 = Ext2::new(cfg).unwrap();
     let mem = ext2.write_to_memory().unwrap();
     // SAFETY: `mem` has a valid pointer and its size.
     let buf = unsafe { std::slice::from_raw_parts(mem.as_ptr(), mem.size()) };
@@ -67,3 +67,19 @@ fn mkfs_empty() {
 
     run_fsck(&path);
 }
+
+#[test]
+fn test_mkfs_empty() {
+    mkfs_empty(&Config {
+        blocks_per_group: 1024,
+        inodes_per_group: 1024,
+    });
+}
+
+#[test]
+fn test_mkfs_empty_more_blocks() {
+    mkfs_empty(&Config {
+        blocks_per_group: 2048,
+        inodes_per_group: 4096,
+    });
+}