Re: [RFC PATCH 15/20] famfs: Add ioctl to file_operations

Jonathan Cameron
2024-02-26T13:44:12Z

On Fri, 23 Feb 2024 11:41:59 -0600
John Groves <John@Groves.net> wrote:

> This commit introduces the per-file ioctl function famfs_file_ioctl()
> into struct file_operations, and introduces the famfs_file_init_dax()
> function (which is called by famfs_file_ioct())
>
> famfs_file_init_dax() associates a dax extent list with a file, making
> it into a proper famfs file. It is called from the FAMFSIOC_MAP_CREATE
> ioctl. Starting with an empty file (which is basically a ramfs file),
> this turns the file into a DAX file backed by the specified extent list.
>
> The other ioctls are:
>
> FAMFSIOC_NOP - A convenient way for user space to verify it's a famfs file
> FAMFSIOC_MAP_GET - Get the header of the metadata for a file
> FAMFSIOC_MAP_GETEXT - Get the extents for a file
>
> The latter two, together, are comparable to xfs_bmap. Our user space tools
> use them primarly in testing.
>
> Signed-off-by: John Groves <john@groves.net>
A few more comments inline. Nothing fundamental just nice to have
simplifications of the code.

> ---
> fs/famfs/famfs_file.c | 226 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 226 insertions(+)
>
> diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
> index 5228e9de1e3b..fd42d5966982 100644
> --- a/fs/famfs/famfs_file.c
> +++ b/fs/famfs/famfs_file.c
> @@ -19,6 +19,231 @@
> #include <uapi/linux/famfs_ioctl.h>
> #include "famfs_internal.h"
>
> +/**
> + * famfs_map_meta_alloc() - Allocate famfs file metadata
> + * @mapp: Pointer to an mcache_map_meta pointer
> + * @ext_count: The number of extents needed
> + */
> +static int
> +famfs_meta_alloc(
> + struct famfs_file_meta **metap,
> + size_t ext_count)
> +{
> + struct famfs_file_meta *meta;
> + size_t metasz;
> +
> + *metap = NULL;

Not responsibility of caller?

> +
> + metasz = sizeof(*meta) + sizeof(*(meta->tfs_extents)) * ext_count;

Looks like struct_size() would be appropriate.

> +
> + meta = kzalloc(metasz, GFP_KERNEL);
> + if (!meta)
> + return -ENOMEM;
> +
> + meta->tfs_extent_ct = ext_count;
> + *metap = meta;
> +
> + return 0;
> +}
> +
> +static void
> +famfs_meta_free(
> + struct famfs_file_meta *map)
> +{
> + kfree(map);
Given this is just kfree you can use __free magic to simplify things below.

> +}
> +
> +/**
> + * famfs_file_init_dax() - FAMFSIOC_MAP_CREATE ioctl handler
> + * @file:
> + * @arg: ptr to struct mcioc_map in user space
> + *
> + * Setup the dax mapping for a file. Files are created empty, and then function is called
> + * (by famfs_file_ioctl()) to setup the mapping and set the file size.
> + */
> +static int
> +famfs_file_init_dax(
> + struct file *file,
> + void __user *arg)
> +{
> + struct famfs_extent *tfs_extents = NULL;
> + struct famfs_file_meta *meta = NULL;
> + struct inode *inode;
> + struct famfs_ioc_map imap;
> + struct famfs_fs_info *fsi;
> + struct super_block *sb;
> + int alignment_errs = 0;
> + size_t extent_total = 0;
> + size_t ext_count;
> + int rc = 0;
> + int i;
> +
> + rc = copy_from_user(&imap, arg, sizeof(imap));
> + if (rc)
> + return -EFAULT;
> +
> + ext_count = imap.ext_list_count;
> + if (ext_count < 1) {
> + rc = -ENOSPC;
> + goto errout;
meta data not yet allocated.
return -ENOSPC;

> + }
> +
> + if (ext_count > FAMFS_MAX_EXTENTS) {
> + rc = -E2BIG;
> + goto errout;
return

> + }
> +
> + inode = file_inode(file);
> + if (!inode) {
> + rc = -EBADF;
> + goto errout;
return;

> + }
> + sb = inode->i_sb;
> + fsi = inode->i_sb->s_fs_info;
> +
> + tfs_extents = &imap.ext_list[0];
> +
> + rc = famfs_meta_alloc(&meta, ext_count);
> + if (rc)
> + goto errout;
return ...

only after this point should there be any
meta data to free on exit?

> +
> + meta->file_type = imap.file_type;
> + meta->file_size = imap.file_size;
> +
> + /* Fill in the internal file metadata structure */
> + for (i = 0; i < imap.ext_list_count; i++) {
> + size_t len;
> + off_t offset;
> +
> + offset = imap.ext_list[i].offset;
> + len = imap.ext_list[i].len;
> +
> + extent_total += len;
> +
> + if (WARN_ON(offset == 0 && meta->file_type != FAMFS_SUPERBLOCK)) {
> + rc = -EINVAL;
> + goto errout;
> + }
> +
> + meta->tfs_extents[i].offset = offset;
> + meta->tfs_extents[i].len = len;
> +
> + /* All extent addresses/offsets must be 2MiB aligned,
> + * and all but the last length must be a 2MiB multiple.
> + */
> + if (!IS_ALIGNED(offset, PMD_SIZE)) {
> + pr_err("%s: error ext %d hpa %lx not aligned\n",
> + __func__, i, offset);
> + alignment_errs++;
> + }
> + if (i < (imap.ext_list_count - 1) && !IS_ALIGNED(len, PMD_SIZE)) {
> + pr_err("%s: error ext %d length %ld not aligned\n",
> + __func__, i, len);
> + alignment_errs++;
> + }
> + }
> +
> + /*
> + * File size can be <= ext list size, since extent sizes are constrained
> + * to PMD multiples
> + */
> + if (imap.file_size > extent_total) {
> + pr_err("%s: file size %lld larger than ext list size %lld\n",
> + __func__, (u64)imap.file_size, (u64)extent_total);
> + rc = -EINVAL;
> + goto errout;
> + }
> +
> + if (alignment_errs > 0) {
> + pr_err("%s: there were %d alignment errors in the extent list\n",
> + __func__, alignment_errs);
> + rc = -EINVAL;
> + goto errout;
> + }
> +
> + /* Publish the famfs metadata on inode->i_private */
> + inode_lock(inode);

Easy to add a guard definition - maybe useful enough to bother as can then do
this which makes the error handling align with other cases.

scoped_guard(inode_sem, inode) {
if (inode->i_private) {
rc = -EEXIST;
goto errout;
}
inode->...

}
> + if (inode->i_private) {
> + rc = -EEXIST; /* file already has famfs metadata */
> + } else {
> + inode->i_private = meta;

You could use __free on the meta data and
inode->i_private = no_ptr_free(meta);
here. Then all your earlier error paths become direct returns.

> + i_size_write(inode, imap.file_size);
> + inode->i_flags |= S_DAX;
> + }
> + inode_unlock(inode);
> +
> + errout:
> + if (rc)
> + famfs_meta_free(meta);
A separate error path is going to be easier to follow as no if (rc)

> +
> + return rc;
> +}
> +
> +/**
> + * famfs_file_ioctl() - top-level famfs file ioctl handler
> + * @file:
> + * @cmd:
> + * @arg:
> + */
> +static
> +long
> +famfs_file_ioctl(
> + struct file *file,
> + unsigned int cmd,
> + unsigned long arg)
> +{
> + long rc;
> +
> + switch (cmd) {
> + case FAMFSIOC_NOP:
> + rc = 0;
return 0;
> + break;
> +
> + case FAMFSIOC_MAP_CREATE:
> + rc = famfs_file_init_dax(file, (void *)arg);
return famfs_file_init_dax()

> + break;
> +
> + case FAMFSIOC_MAP_GET: {
> + struct inode *inode = file_inode(file);
> + struct famfs_file_meta *meta = inode->i_private;
> + struct famfs_ioc_map umeta;
> +
> + memset(&umeta, 0, sizeof(umeta));
> +
> + if (meta) {
> + /* TODO: do more to harmonize these structures */
> + umeta.extent_type = meta->tfs_extent_type;
> + umeta.file_size = i_size_read(inode);
> + umeta.ext_list_count = meta->tfs_extent_ct;
> +
> + rc = copy_to_user((void __user *)arg, &umeta, sizeof(umeta));
> + if (rc)
> + pr_err("%s: copy_to_user returned %ld\n", __func__, rc);
> +
> + } else {
> + rc = -EINVAL;
> + }
Flip logic.

if (!meta)
return -EINVAL;

umeta ...
return 0;

> + }
> + break;
> + case FAMFSIOC_MAP_GETEXT: {
> + struct inode *inode = file_inode(file);
> + struct famfs_file_meta *meta = inode->i_private;
> +
> + if (meta)
> + rc = copy_to_user((void __user *)arg, meta->tfs_extents,
> + meta->tfs_extent_ct * sizeof(struct famfs_extent));
> + else
> + rc = -EINVAL;
if (!meta)
return -EINVAL;

return copy_to_user

> + }
> + break;
> + default:
> + rc = -ENOTTY;
return -ENOTTY;

> + break;
> + }
> +
> + return rc;
Early returns will simplify the flow for anyone reading this.

> +}