[RFC] fsinfo: Add a system call to allow querying of filesystem information
Add a system call to allow filesystem information to be queried. This is
implemented as a function switch where the desired attribute value or
values is nominated.
===============
NEW SYSTEM CALL
===============
The new system call looks like:
int ret = fsinfo(int dfd,
const char *filename,
const struct fsinfo_params *params,
void *buffer,
size_t buf_size);
The params parameter optionally points to a block of parameters:
struct fsinfo_params {
enum fsinfo_attribute request;
__u32 Nth;
__u32 Mth;
__u32 at_flags;
__u32 __reserved[6];
};
If params is NULL, it is assumed params->request should be
fsinfo_attr_statfs, params->Nth should be 0, params->Mth should be 0 and
params->at_flags should be 0.
If params is given, all of params->__reserved[] must be 0.
dfd, filename and params->at_flags indicate the file to query. There is no
equivalent of lstat() as that can be emulated with fsinfo() by setting
AT_SYMLINK_NOFOLLOW in params->at_flags. There is also no equivalent of
fstat() as that can be emulated by passing a NULL filename to fsinfo() with
the fd of interest in dfd. AT_NO_AUTOMOUNT can also be used to an allow
automount point to be queried without triggering it.
AT_FORCE_ATTR_SYNC can be set in params->at_flags. This will require a
network filesystem to synchronise its attributes with the server.
AT_NO_ATTR_SYNC can be set in params->at_flags. This will suppress
synchronisation with the server in a network filesystem. The resulting
values should be considered approximate.
params->request indicates the attribute/attributes to be queried. This can
be one of:
fsinfo_attr_statfs - statfs-style info
fsinfo_attr_fsinfo - Information about fsinfo()
fsinfo_attr_ids - Filesystem IDs
fsinfo_attr_limits - Filesystem limits
fsinfo_attr_supports - What's supported in statx(), IOC flags
fsinfo_attr_capabilities - Filesystem capabilities
fsinfo_attr_timestamp_info - Inode timestamp info
fsinfo_attr_volume_id - Volume ID (string)
fsinfo_attr_volume_uuid - Volume UUID
fsinfo_attr_volume_name - Volume name (string)
fsinfo_attr_cell_name - Cell name (string)
fsinfo_attr_domain_name - Domain name (string)
fsinfo_attr_realm_name - Realm name (string)
fsinfo_attr_server_name - Name of the Nth server (string)
fsinfo_attr_server_address - Mth address of the Nth server
fsinfo_attr_error_state - Error state
fsinfo_attr_parameter - Nth mount parameter (string)
fsinfo_attr_source - Nth mount source name (string)
fsinfo_attr_name_encoding - Filename encoding (string)
fsinfo_attr_name_codepage - Filename codepage (string)
fsinfo_attr_io_size - Optimal I/O sizes
Some attributes (such as the servers backing a network filesystem) can have
multiple values. These can be enumerated by setting params->Nth and
params->Mth to 0, 1, ... until ENODATA is returned.
buffer and buf_size point to the reply buffer. The buffer is filled up to the
specified size, even if this means truncating the reply. The full size of the
reply is returned. In future versions, this will allow extra fields to be
tacked on to the end of the reply, but anyone not expecting them will only get
the subset they're expecting. If either buffer of buf_size are 0, no copy
will take place and the data size will be returned.
At the moment, this will only work on x86_64 and i386 as it requires the system
call to be wired up.
Signed-off-by: David Howells <dhowells@redhat.com>
9 files changed
