Add fsparam_fd("source") so that userspace can pass an already-opened
file descriptor instead of a path string. When the fd is provided via
fsconfig(FSCONFIG_SET_FD, "source", NULL, fd), it is stored directly
in sbi->dif0.file and erofs_fc_get_tree() skips the filp_open() call.
This is useful for mount namespaces where the backing file may not be
reachable by path, and for tools that already hold an fd to the image
(e.g. composefs reusing an erofs mount's backing file).
Signed-off-by: Giuseppe Scrivano <[email protected]>
---
I've moved this out of the previous series, as the second patch is on
hold for a design discussion. Since the two patches were independent,
they do not need to be held together.
v1: https://lore.kernel.org/linux-fsdevel/ak5GfvVfWLJU1EwK@debian/#r
fs/erofs/super.c | 36 ++++++++++++++++++++++++------------
1 file changed, 24 insertions(+), 12 deletions(-)
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 86fa5c6a0c70..3040d4cf9b85 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -386,6 +386,7 @@ static void erofs_default_options(struct erofs_sb_info *sbi)
enum {
Opt_user_xattr, Opt_acl, Opt_cache_strategy, Opt_dax, Opt_dax_enum,
Opt_device, Opt_domain_id, Opt_directio, Opt_fsoffset, Opt_inode_share,
+ Opt_source_fd,
};
static const struct constant_table erofs_param_cache_strategy[] = {
@@ -413,6 +414,7 @@ static const struct fs_parameter_spec erofs_fs_parameters[]
= {
fsparam_flag_no("directio", Opt_directio),
fsparam_u64("fsoffset", Opt_fsoffset),
fsparam_flag("inode_share", Opt_inode_share),
+ fsparam_fd("source", Opt_source_fd),
{}
};
@@ -524,6 +526,11 @@ static int erofs_fc_parse_param(struct fs_context *fc,
else
set_opt(&sbi->opt, INODE_SHARE);
break;
+ case Opt_source_fd:
+ if (sbi->dif0.file)
+ return -EINVAL;
+ sbi->dif0.file = get_file(param->file);
+ break;
}
return 0;
}
@@ -752,14 +759,18 @@ static int erofs_fc_fill_super(struct super_block *sb,
struct fs_context *fc)
static int erofs_fc_get_tree(struct fs_context *fc)
{
- int ret;
+ struct erofs_sb_info *sbi = fc->s_fs_info;
+ struct file *file = sbi->dif0.file;
- ret = get_tree_bdev_flags(fc, erofs_fc_fill_super,
- IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) ?
- GET_TREE_BDEV_QUIET_LOOKUP : 0);
- if (IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) && ret == -ENOTBLK) {
- struct erofs_sb_info *sbi = fc->s_fs_info;
- struct file *file;
+ if (!IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) || !file) {
+ int ret;
+
+ ret = get_tree_bdev_flags(fc, erofs_fc_fill_super,
+ IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) ?
+ GET_TREE_BDEV_QUIET_LOOKUP : 0);
+ if (!IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) ||
+ ret != -ENOTBLK)
+ return ret;
if (!fc->source)
return invalf(fc, "No source specified");
@@ -767,12 +778,13 @@ static int erofs_fc_get_tree(struct fs_context *fc)
if (IS_ERR(file))
return PTR_ERR(file);
sbi->dif0.file = file;
-
- if (S_ISREG(file_inode(sbi->dif0.file)->i_mode) &&
- sbi->dif0.file->f_mapping->a_ops->read_folio)
- return get_tree_nodev(fc, erofs_fc_fill_super);
}
- return ret;
+ if (!S_ISREG(file_inode(file)->i_mode) ||
+ !file->f_mapping->a_ops->read_folio) {
+ errorfc(fc, "source is unsupported");
+ return -EINVAL;
+ }
+ return get_tree_nodev(fc, erofs_fc_fill_super);
}
static int erofs_fc_reconfigure(struct fs_context *fc)
--
2.55.0
