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

[Qu Wenruo]

On 2022/6/30 18:06, Simon Glass wrote:
On Tue, 28 Jun 2022 at 01:28, Qu Wenruo <w...@suse.com> wrote:

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(-)

Reviewed-by: Simon Glass <s...@chromium.org>

with a comment as requested below


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);

Please add a full comment.

This is already removed in the formal version:
https://patchwork.kernel.org/project/linux-btrfs/list/?series=654990

As sandbox is just calling host OS read() to handle IO, thus it doesn't 
need to bother the alignment at all.

Thanks,
Qu


  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


Regards,
Simon