[PATCH RFC 6/8] fs: sandboxfs: add sandbox_fs_get_blocksize()

[Qu Wenruo via Linux-erofs]

This is to make sandboxfs to report blocksize it supports for
_fs_read() to handle unaligned read.

Unlike all other fses, sandboxfs can handle unaligned read/write without
any problem since it's calling read()/write(), which doesn't bother the
blocksize at all.

This change is mostly to make testing of _fs_read() much easier.

Cc: Simon Glass <s...@chromium.org>
Signed-off-by: Qu Wenruo <w...@suse.com>
---
 arch/sandbox/cpu/os.c  | 11 +++++++++++
 fs/fs.c                |  2 +-
 fs/sandbox/sandboxfs.c | 14 ++++++++++++++
 include/os.h           |  8 ++++++++
 include/sandboxfs.h    |  1 +
 5 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/arch/sandbox/cpu/os.c b/arch/sandbox/cpu/os.c
index 5ea54179176c..6c29f29bdd9b 100644
--- a/arch/sandbox/cpu/os.c
+++ b/arch/sandbox/cpu/os.c
@@ -46,6 +46,17 @@ ssize_t os_read(int fd, void *buf, size_t count)
        return read(fd, buf, count);
 }
 
+ssize_t os_get_blocksize(int fd)
+{
+       struct stat stat = {0};
+       int ret;
+
+       ret = fstat(fd, &stat);
+       if (ret < 0)
+               return -errno;
+       return stat.st_blksize;
+}
+
 ssize_t os_write(int fd, const void *buf, size_t count)
 {
        return write(fd, buf, count);
diff --git a/fs/fs.c b/fs/fs.c
index 7e4ead9b790b..337d5711c28c 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -261,7 +261,7 @@ static struct fstype_info fstypes[] = {
                .exists = sandbox_fs_exists,
                .size = sandbox_fs_size,
                .read = fs_read_sandbox,
-               .get_blocksize = fs_get_blocksize_unsupported,
+               .get_blocksize = sandbox_fs_get_blocksize,
                .write = fs_write_sandbox,
                .uuid = fs_uuid_unsupported,
                .opendir = fs_opendir_unsupported,
diff --git a/fs/sandbox/sandboxfs.c b/fs/sandbox/sandboxfs.c
index 4ae41d5b4db1..130fee088621 100644
--- a/fs/sandbox/sandboxfs.c
+++ b/fs/sandbox/sandboxfs.c
@@ -55,6 +55,20 @@ int sandbox_fs_read_at(const char *filename, loff_t pos, 
void *buffer,
        return ret;
 }
 
+int sandbox_fs_get_blocksize(const char *filename)
+{
+       int fd;
+       int ret;
+
+       fd = os_open(filename, OS_O_RDONLY);
+       if (fd < 0)
+               return fd;
+
+       ret = os_get_blocksize(fd);
+       os_close(fd);
+       return ret;
+}
+
 int sandbox_fs_write_at(const char *filename, loff_t pos, void *buffer,
                        loff_t towrite, loff_t *actwrite)
 {
diff --git a/include/os.h b/include/os.h
index 10e198cf503e..a864d9ca39b2 100644
--- a/include/os.h
+++ b/include/os.h
@@ -26,6 +26,14 @@ struct sandbox_state;
  */
 ssize_t os_read(int fd, void *buf, size_t count);
 
+/**
+ * Get the optimial blocksize through stat() call.
+ *
+ * @fd:                File descriptor as returned by os_open()
+ * Return:     >=0 for the blocksize. <0 for error.
+ */
+ssize_t os_get_blocksize(int fd);
+
 /**
  * Access to the OS write() system call
  *
diff --git a/include/sandboxfs.h b/include/sandboxfs.h
index 783dd5c88a73..6937068f7b82 100644
--- a/include/sandboxfs.h
+++ b/include/sandboxfs.h
@@ -32,6 +32,7 @@ void sandbox_fs_close(void);
 int sandbox_fs_ls(const char *dirname);
 int sandbox_fs_exists(const char *filename);
 int sandbox_fs_size(const char *filename, loff_t *size);
+int sandbox_fs_get_blocksize(const char *filename);
 int fs_read_sandbox(const char *filename, void *buf, loff_t offset, loff_t len,
                    loff_t *actread);
 int fs_write_sandbox(const char *filename, void *buf, loff_t offset,
-- 
2.36.1