Add a manual page to document the fsinfo() system call.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---
man2/fsinfo.2 | 1017 +++++++++++++++++++++++++++++++++++++++++++++++++++
man2/ioctl_iflags.2 | 6
man2/stat.2 | 7
man2/statx.2 | 13 +
man2/utime.2 | 7
man2/utimensat.2 | 7
6 files changed, 1057 insertions(+)
create mode 100644 man2/fsinfo.2
diff --git a/man2/fsinfo.2 b/man2/fsinfo.2
new file mode 100644
index 000000000..5710232df
--- /dev/null
+++ b/man2/fsinfo.2
@@ -0,0 +1,1017 @@
+'\" t
+.\" Copyright (c) 2018 David Howells <dhowells@xxxxxxxxxx>
+.\"
+.\" %%%LICENSE_START(VERBATIM)
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of this
+.\" manual under the conditions for verbatim copying, provided that the
+.\" entire resulting derived work is distributed under the terms of a
+.\" permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date. The author(s) assume no
+.\" responsibility for errors or omissions, or for damages resulting from
+.\" the use of the information contained herein. The author(s) may not
+.\" have taken the same level of care in the production of this manual,
+.\" which is licensed free of charge, as they might when working
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
+.\"
+.TH FSINFO 2 2018-06-06 "Linux" "Linux Programmer's Manual"
+.SH NAME
+fsinfo \- Get filesystem information
+.SH SYNOPSIS
+.nf
+.B #include <sys/types.h>
+.br
+.B #include <sys/fsinfo.h>
+.br
+.B #include <unistd.h>
+.br
+.BR "#include <fcntl.h> " "/* Definition of AT_* constants */"
+.PP
+.BI "int fsinfo(int " dirfd ", const char *" pathname ","
+.BI " struct fsinfo_params *" params ","
+.BI " void *" buffer ", size_t " buf_size );
+.fi
+.PP
+.IR Note :
+There is no glibc wrapper for
+.BR fsinfo ();
+see NOTES.
+.SH DESCRIPTION
+.PP
+fsinfo() retrieves the desired filesystem attribute, as selected by the
+parameters pointed to by
+.IR params ,
+and stores its value in the buffer pointed to by
+.IR buffer .
+.PP
+The parameter structure is optional, defaulting to all the parameters being 0
+if the pointer is NULL. The structure looks like the following:
+.PP
+.in +4n
+.nf
+struct fsinfo_params {
+ __u32 at_flags; /* AT_SYMLINK_NOFOLLOW and similar flags */
+ __u32 request; /* Requested attribute */
+ __u32 Nth; /* Instance of attribute */
+ __u32 Mth; /* Subinstance of Nth instance */
+ __u32 __reserved[6]; /* Reserved params; all must be 0 */
+};
+.fi
+.in
+.PP
+The filesystem to be queried is looked up using a combination of
+.IR dfd ", " pathname " and " params->at_flags.
+This is discussed in more detail below.
+.PP
+The desired attribute is indicated by
+.IR params->request .
+If
+.I params
+is NULL, this will default to
+.BR fsinfo_attr_statfs ,
+which retrieves some of the information returned by
+.BR statfs ().
+The available attributes are described below in the "THE ATTRIBUTES" section.
+.PP
+Some attributes can have multiple values and some can even have multiple
+instances with multiple values. For example, a network filesystem might use
+multiple servers. The names of each of these servers can be retrieved by
+using
+.I params->Nth
+to iterate through all the instances until error
+.B ENODATA
+occurs, indicating the end of the list. Further, each server might have
+multiple addresses available; these can be enumerated using
+.I params->Nth
+to iterate the servers and
+.I params->Mth
+to iterate the addresses of the Nth server.
+.PP
+The amount of data written into the buffer depends on the attribute selected.
+Some attributes return variable-length strings and some return fixed-size
+structures. If either
+.IR buffer " is NULL or " buf_size " is 0"
+then the size of the attribute value will be returned and nothing will be
+written into the buffer.
+.PP
+The
+.I params->__reserved
+parameters must all be 0.
+.\"_______________________________________________________
+.SS
+Allowance for Future Attribute Expansion
+.PP
+To allow for the future expansion and addition of fields to any fixed-size
+structure attribute,
+.BR fsinfo ()
+makes the following guarantees:
+.RS 4m
+.IP (1) 4m
+It will always clear any excess space in the buffer.
+.IP (2) 4m
+It will always return the actual size of the data.
+.IP (3) 4m
+It will truncate the data to fit it into the buffer rather than giving an
+error.
+.IP (4) 4m
+Any new version of a structure will incorporate all the fields from the old
+version at same offsets.
+.RE
+.PP
+So, for example, if the caller is running on an older version of the kernel
+with an older, smaller version of the structure than was asked for, the kernel
+will write the smaller version into the buffer and will clear the remainder of
+the buffer to make sure any additional fields are set to 0. The function will
+return the actual size of the data.
+.PP
+On the other hand, if the caller is running on a newer version of the kernel
+with a newer version of the structure that is larger than the buffer, the write
+to the buffer will be truncated to fit as necessary and the actual size of the
+data will be returned.
+.PP
+Note that this doesn't apply to variable-length string attributes.
+
+.\"_______________________________________________________
+.SS
+Invoking \fBfsinfo\fR():
+.PP
+To access a file's status, no permissions are required on the file itself, but
+in the case of
+.BR fsinfo ()
+with a path, execute (search) permission is required on all of the directories
+in
+.I pathname
+that lead to the file.
+.PP
+.BR fsinfo ()
+uses
+.IR pathname ", " dirfd " and " params->at_flags
+to locate the target file in one of a variety of ways:
+.TP
+[*] By absolute path.
+.I pathname
+points to an absolute path and
+.I dirfd
+is ignored. The file is looked up by name, starting from the root of the
+filesystem as seen by the calling process.
+.TP
+[*] By cwd-relative path.
+.I pathname
+points to a relative path and
+.IR dirfd " is " AT_FDCWD .
+The file is looked up by name, starting from the current working directory.
+.TP
+[*] By dir-relative path.
+.I pathname
+points to relative path and
+.I dirfd
+indicates a file descriptor pointing to a directory. The file is looked up by
+name, starting from the directory specified by
+.IR dirfd .
+.TP
+[*] By file descriptor.
+.IR pathname " is " NULL " and " dirfd
+indicates a file descriptor. The file attached to the file descriptor is
+queried directly. The file descriptor may point to any type of file, not just
+a directory.
+.PP
+.I flags
+can be used to influence a path-based lookup. A value for
+.I flags
+is constructed by OR'ing together zero or more of the following constants:
+.TP
+.BR AT_EMPTY_PATH
+.\" commit 65cfc6722361570bfe255698d9cd4dccaf47570d
+If
+.I pathname
+is an empty string, operate on the file referred to by
+.IR dirfd
+(which may have been obtained using the
+.BR open (2)
+.B O_PATH
+flag).
+If
+.I dirfd
+is
+.BR AT_FDCWD ,
+the call operates on the current working directory.
+In this case,
+.I dirfd
+can refer to any type of file, not just a directory.
+This flag is Linux-specific; define
+.B _GNU_SOURCE
+.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
+to obtain its definition.
+.TP
+.BR AT_NO_AUTOMOUNT
+Don't automount the terminal ("basename") component of
+.I pathname
+if it is a directory that is an automount point. This allows the caller to
+gather attributes of the filesystem holding an automount point (rather than
+the filesystem it would mount). This flag can be used in tools that scan
+directories to prevent mass-automounting of a directory of automount points.
+The
+.B AT_NO_AUTOMOUNT
+flag has no effect if the mount point has already been mounted over.
+This flag is Linux-specific; define
+.B _GNU_SOURCE
+.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
+to obtain its definition.
+.TP
+.B AT_SYMLINK_NOFOLLOW
+If
+.I pathname
+is a symbolic link, do not dereference it:
+instead return information about the link itself, like
+.BR lstat ().
+.SH THE ATTRIBUTES
+.PP
+There is a range of attributes that can be selected from. These are:
+
+.\" __________________ fsinfo_attr_statfs __________________
+.TP
+.B fsinfo_attr_statfs
+This retrieves the "dynamic"
+.B statfs
+information, such as block and file counts, that are expected to change whilst
+a filesystem is being used. This fills in the following structure:
+.PP
+.RS
+.in +4n
+.nf
+struct fsinfo_statfs {
+ __u64 f_blocks; /* Total number of blocks in fs */
+ __u64 f_bfree; /* Total number of free blocks */
+ __u64 f_bavail; /* Number of free blocks available to ordinary user */
+ __u64 f_files; /* Total number of file nodes in fs */
+ __u64 f_ffree; /* Number of free file nodes */
+ __u64 f_favail; /* Number of free file nodes available to ordinary user */
+ __u32 f_bsize; /* Optimal block size */
+ __u32 f_frsize; /* Fragment size */
+};
+.fi
+.in
+.RE
+.IP
+The fields correspond to those of the same name returned by
+.BR statfs ().
+
+.\" __________________ fsinfo_attr_fsinfo __________________
+.TP
+.B fsinfo_attr_fsinfo
+This retrieves information about the
+.BR fsinfo ()
+system call itself. This fills in the following structure:
+.PP
+.RS
+.in +4n
+.nf
+struct fsinfo_fsinfo {
+ __u32 max_attr;
+ __u32 max_cap;
+};
+.fi
+.in
+.RE
+.IP
+The
+.I max_attr
+value indicates the number of attributes supported by the
+.BR fsinfo ()
+system call, and
+.I max_cap
+indicates the number of capability bits supported by the
+.B fsinfo_attr_capabilities
+attribute. The first corresponds to
+.I fsinfo_attr__nr
+and the second to
+.I fsinfo_cap__nr
+in the header file.
+
+.\" __________________ fsinfo_attr_ids __________________
+.TP
+.B fsinfo_attr_ids
+This retrieves a number of fixed IDs and other static information otherwise
+available through
+.BR statfs ().
+The following structure is filled in:
+.PP
+.RS
+.in +4n
+.nf
+struct fsinfo_ids {
+ char f_fs_name[15 + 1]; /* Filesystem name */
+ __u64 f_flags; /* Filesystem mount flags (MS_*) */
+ __u64 f_fsid; /* Short 64-bit Filesystem ID */
+ __u64 f_sb_id; /* Internal superblock ID */
+ __u32 f_fstype; /* Filesystem type from linux/magic.h */
+ __u32 f_dev_major; /* As st_dev_* from struct statx */
+ __u32 f_dev_minor;
+};
+.fi
+.in
+.RE
+.IP
+Most of these are filled in as for
+.BR statfs (),
+with the addition of the filesystem's symbolic name in
+.I f_fs_name
+and an identifier for use in notifications in
+.IR f_sb_id .
+
+.\" __________________ fsinfo_attr_limits __________________
+.TP
+.B fsinfo_attr_limits
+This retrieves information about the limits of what a filesystem can support.
+The following structure is filled in:
+.PP
+.RS
+.in +4n
+.nf
+struct fsinfo_limits {
+ __u64 max_file_size;
+ __u64 max_uid;
+ __u64 max_gid;
+ __u64 max_projid;
+ __u32 max_dev_major;
+ __u32 max_dev_minor;
+ __u32 max_hard_links;
+ __u32 max_xattr_body_len;
+ __u16 max_xattr_name_len;
+ __u16 max_filename_len;
+ __u16 max_symlink_len;
+ __u16 __reserved[1];
+};
+.fi
+.in
+.RE
+.IP
+These indicate the maximum supported sizes for a variety of filesystem objects,
+including the file size, the extended attribute name length and body length,
+the filename length and the symlink body length.
+.IP
+It also indicates the maximum representable values for a User ID, a Group ID,
+a Project ID, a device major number and a device minor number.
+.IP
+And finally, it indicates the maximum number of hard links that can be made to
+a file.
+.IP
+Note that some of these values may be zero if the underlying object or concept
+is not supported by the filesystem or the medium.
+
+.\" __________________ fsinfo_attr_supports __________________
+.TP
+.B fsinfo_attr_supports
+This retrieves information about what bits a filesystem supports in various
+masks. The following structure is filled in:
+.PP
+.RS
+.in +4n
+.nf
+struct fsinfo_supports {
+ __u64 stx_attributes;
+ __u32 stx_mask;
+ __u32 ioc_flags;
+ __u32 win_file_attrs;
+ __u32 __reserved[1];
+};
+.fi
+.in
+.RE
+.IP
+The
+.IR stx_attributes " and " stx_mask
+fields indicate what bits in the struct statx fields of the matching names
+are supported by the filesystem.
+.IP
+The
+.I ioc_flags
+field indicates what FS_*_FL flag bits as used through the FS_IOC_GET/SETFLAGS
+ioctls are supported by the filesystem.
+.IP
+The
+.I win_file_attrs
+indicates what DOS/Windows file attributes a filesystem supports, if any.
+
+.\" __________________ fsinfo_attr_capabilities __________________
+.TP
+.B fsinfo_attr_capabilities
+This retrieves information about what features a filesystem supports as a
+series of single bit indicators. The following structure is filled in:
+.PP
+.RS
+.in +4n
+.nf
+struct fsinfo_capabilities {
+ __u8 capabilities[(fsinfo_cap__nr + 7) / 8];
+};
+.fi
+.in
+.RE
+.IP
+where the bit of interest can be found by:
+.PP
+.RS
+.in +4n
+.nf
+ p->capabilities[bit / 8] & (1 << (bit % 8)))
+.fi
+.in
+.RE
+.IP
+The bits are listed by
+.I enum fsinfo_capability
+and
+.B fsinfo_cap__nr
+is one more than the last capability bit listed in the header file.
+.IP
+Note that the number of capability bits actually supported by the kernel can be
+found using the
+.B fsinfo_attr_fsinfo
+attribute.
+.IP
+The capability bits and their meanings are listed below in the "THE
+CAPABILITIES" section.
+
+.\" __________________ fsinfo_attr_timestamp_info __________________
+.TP
+.B fsinfo_attr_timestamp_info
+This retrieves information about what timestamp resolution and scope is
+supported by a filesystem for each of the file timestamps. The following
+structure is filled in:
+.PP
+.RS
+.in +4n
+.nf
+struct fsinfo_timestamp_info {
+ __s64 minimum_timestamp;
+ __s64 maximum_timestamp;
+ __u16 atime_gran_mantissa;
+ __u16 btime_gran_mantissa;
+ __u16 ctime_gran_mantissa;
+ __u16 mtime_gran_mantissa;
+ __s8 atime_gran_exponent;
+ __s8 btime_gran_exponent;
+ __s8 ctime_gran_exponent;
+ __s8 mtime_gran_exponent;
+ __u32 __reserved[1];
+};
+.fi
+.in
+.RE
+.IP
+where
+.IR minimum_timestamp " and " maximum_timestamp
+are the limits on the timestamps that the filesystem supports and
+.IR *time_gran_mantissa " and " *time_gran_exponent
+indicate the granularity of each timestamp in terms of seconds, using the
+formula:
+.PP
+.RS
+.in +4n
+.nf
+mantissa * pow(10, exponent) Seconds
+.fi
+.in
+.RE
+.IP
+where exponent may be negative and the result may be a fraction of a second.
+.IP
+Four timestamps are detailed: \fBA\fPccess time, \fBB\fPirth/creation time,
+\fBC\fPhange time and \fBM\fPodification time. Capability bits are defined
+that specify whether each of these exist in the filesystem or not.
+.IP
+Note that the timestamp description may be approximated or inaccurate if the
+file is actually remote or is the union of multiple objects.
+
+.\" __________________ fsinfo_attr_volume_id __________________
+.TP
+.B fsinfo_attr_volume_id
+This retrieves the system's superblock volume identifier as a variable-length
+string. This does not necessarily represent a value stored in the medium but
+might be constructed on the fly.
+.IP
+For instance, for a block device this is the block device identifier
+(eg. "sdb2"); for AFS this would be the numeric volume identifier.
+
+.\" __________________ fsinfo_attr_volume_uuid __________________
+.TP
+.B fsinfo_attr_volume_uuid
+This retrieves the volume UUID, if there is one, as a little-endian binary
+UUID. This fills in the following structure:
+.PP
+.RS
+.in +4n
+.nf
+struct fsinfo_volume_uuid {
+ __u8 uuid[16];
+};
+.fi
+.in
+.RE
+.IP
+
+.\" __________________ fsinfo_attr_volume_name __________________
+.TP
+.B fsinfo_attr_volume_name
+This retrieves the filesystem's volume name as a variable-length string. This
+is expected to represent a name stored in the medium.
+.IP
+For a block device, this might be a label stored in the superblock. For a
+network filesystem, this might be a logical volume name of some sort.
+
+.\" __________________ fsinfo_attr_cell/domain __________________
+.PP
+.B fsinfo_attr_cell_name
+.br
+.B fsinfo_attr_domain_name
+.br
+.IP
+These two attributes are variable-length string attributes that may be used to
+obtain information about network filesystems. An AFS volume, for instance,
+belongs to a named cell. CIFS shares may belong to a domain.
+
+.\" __________________ fsinfo_attr_realm_name __________________
+.TP
+.B fsinfo_attr_realm_name
+This attribute is variable-length string that indicates the Kerberos realm that
+a filesystem's authentication tokens should come from.
+
+.\" __________________ fsinfo_attr_server_name __________________
+.TP
+.B fsinfo_attr_server_name
+This attribute is a multiple-value attribute that lists the names of the
+servers that are backing a network filesystem. Each value is a variable-length
+string. The values are enumerated by calling
+.BR fsinfo ()
+multiple times, incrementing
+.I params->Nth
+each time until an ENODATA error occurs, thereby indicating the end of the
+list.
+
+.\" __________________ fsinfo_attr_server_address __________________
+.TP
+.B fsinfo_attr_server_address
+This attribute is a multiple-instance, multiple-value attribute that lists the
+addresses of the servers that are backing a network filesystem. Each value is
+a structure of the following type:
+.PP
+.RS
+.in +4n
+.nf
+struct fsinfo_server_address {
+ struct __kernel_sockaddr_storage address;
+};
+.fi
+.in
+.RE
+.IP
+Where the address may be AF_INET, AF_INET6, AF_RXRPC or any other type as
+appropriate to the filesystem.
+.IP
+The values are enumerated by calling
+.IR fsinfo ()
+multiple times, incrementing
+.I params->Nth
+to step through the servers and
+.I params->Mth
+to step through the addresses of the Nth server each time until ENODATA errors
+occur, thereby indicating either the end of a server's address list or the end
+of the server list.
+.IP
+Barring the server list changing whilst being accessed, it is expected that the
+.I params->Nth
+will correspond to
+.I params->Nth
+for
+.BR fsinfo_attr_server_name .
+
+.\" __________________ fsinfo_attr_parameter __________________
+.TP
+.B fsinfo_attr_parameter
+This attribute is a multiple-value attribute that lists the values of the mount
+parameters for a filesystem as variable-length strings.
+.IP
+The parameters are enumerated by calling
+.BR fsinfo ()
+multiple times, incrementing
+.I params->Nth
+to step through them until error ENODATA is given.
+.IP
+Parameter strings are presented in a form akin to the way they're passed to the
+context created by the
+.BR fsopen ()
+system call. For example, straight text parameters will be rendered as
+something like:
+.PP
+.RS
+.in +4n
+.nf
+"o data=journal"
+"o noquota"
+.fi
+.in
+.RE
+.IP
+Where the initial "word" indicates the option form.
+
+.\" __________________ fsinfo_attr_source __________________
+.TP
+.B fsinfo_attr_source
+This attribute is a multiple-value attribute that lists the mount sources for a
+filesystem as variable-length strings. Normally only one source will be
+available, but the possibility of having more than one is allowed for.
+.IP
+The sources are enumerated by calling
+.BR fsinfo ()
+multiple times, incrementing
+.I params->Nth
+to step through them until error ENODATA is given.
+.IP
+Source strings are presented in a form akin to the way they're passed to the
+context created by the
+.BR fsopen ()
+system call. For example, they will be rendered as something like:
+.PP
+.RS
+.in +4n
+.nf
+"s /dev/sda1"
+"s example.com/pub/linux/"
+.fi
+.in
+.RE
+.IP
+Where the initial "word" indicates the option form.
+
+.\" __________________ fsinfo_attr_name_encoding __________________
+.TP
+.B fsinfo_attr_name_encoding
+This attribute is variable-length string that indicates the filename encoding
+used by the filesystem. The default is "utf8". Note that this may indicate a
+non-8-bit encoding if that's what the underlying filesystem actually supports.
+
+.\" __________________ fsinfo_attr_name_codepage __________________
+.TP
+.B fsinfo_attr_name_codepage
+This attribute is variable-length string that indicates the codepage used to
+translate filenames from the filesystem to the system if this is applicable to
+the filesystem.
+
+.\" __________________ fsinfo_attr_io_size __________________
+.TP
+.B fsinfo_attr_io_size
+This retrieves information about the I/O sizes supported by the filesystem.
+The following structure is filled in:
+.PP
+.RS
+.in +4n
+.nf
+struct fsinfo_io_size {
+ __u32 block_size;
+ __u32 max_single_read_size;
+ __u32 max_single_write_size;
+ __u32 best_read_size;
+ __u32 best_write_size;
+};
+.fi
+.in
+.RE
+.IP
+Where
+.I block_size
+indicates the fundamental I/O block size of the filesystem as something
+O_DIRECT read/write sizes must be a multiple of;
+.IR max_single_write_size " and " max_single_write_size
+indicate the maximum sizes for individual unbuffered data transfer operations;
+and
+.IR best_read_size " and " best_write_size
+indicate the recommended I/O sizes.
+.IP
+Note that any of these may be zero if inapplicable or indeterminable.
+
+
+
+.SH THE CAPABILITIES
+.PP
+There are number of capability bits in a bit array that can be retrieved using
+.BR fsinfo_attr_capabilities .
+These give information about features of the filesystem driver and the specific
+filesystem.
+
+.\" __________________ fsinfo_cap_is_*_fs __________________
+.PP
+.B fsinfo_cap_is_kernel_fs
+.br
+.B fsinfo_cap_is_block_fs
+.br
+.B fsinfo_cap_is_flash_fs
+.br
+.B fsinfo_cap_is_network_fs
+.br
+.B fsinfo_cap_is_automounter_fs
+.IP
+These indicate the primary type of the filesystem.
+.B kernel
+filesystems are special communication interfaces that substitute files for
+system calls; examples include procfs and sysfs.
+.B block
+filesystems require a block device on which to operate; examples include ext4
+and XFS.
+.B flash
+filesystems require an MTD device on which to operate; examples include JFFS2.
+.B network
+filesystems require access to the network and contact one or more servers;
+examples include NFS and AFS.
+.B automounter
+filesystems are kernel special filesystems that host automount points and
+triggers to dynamically create automount points. Examples include autofs and
+AFS's dynamic root.
+
+.\" __________________ fsinfo_cap_automounts __________________
+.TP
+.B fsinfo_cap_automounts
+The filesystem may have automount points that can be triggered by pathwalk.
+
+.\" __________________ fsinfo_cap_adv_locks __________________
+.TP
+.B fsinfo_cap_adv_locks
+The filesystem supports advisory file locks. For a network filesystem, this
+indicates that the advisory file locks are cross-client (and also between
+server and its local filesystem on something like NFS).
+
+.\" __________________ fsinfo_cap_mand_locks __________________
+.TP
+.B fsinfo_cap_mand_locks
+The filesystem supports mandatory file locks. For a network filesystem, this
+indicates that the mandatory file locks are cross-client (and also between
+server and its local filesystem on something like NFS).
+
+.\" __________________ fsinfo_cap_leases __________________
+.TP
+.B fsinfo_cap_leases
+The filesystem supports leases. For a network filesystem, this means that the
+server will tell the client to clean up its state on a file before passing the
+lease to another client.
+
+.\" __________________ fsinfo_cap_*ids __________________
+.PP
+.B fsinfo_cap_uids
+.br
+.B fsinfo_cap_gids
+.br
+.B fsinfo_cap_projids
+.IP
+These indicate that the filesystem supports numeric user IDs, group IDs and
+project IDs respectively.
+
+.\" __________________ fsinfo_cap_id_* __________________
+.PP
+.B fsinfo_cap_id_names
+.br
+.B fsinfo_cap_id_guids
+.IP
+These indicate that the filesystem employs textual names and/or GUIDs as
+identifiers.
+
+.\" __________________ fsinfo_cap_windows_attrs __________________
+.TP
+.B fsinfo_cap_windows_attrs
+Indicates that the filesystem supports some Windows FILE_* attributes.
+
+.\" __________________ fsinfo_cap_*_quotas __________________
+.PP
+.B fsinfo_cap_user_quotas
+.br
+.B fsinfo_cap_group_quotas
+.br
+.B fsinfo_cap_project_quotas
+.IP
+These indicate that the filesystem supports quotas for users, groups and
+projects respectively.
+
+.\" __________________ fsinfo_cap_xattrs/filetypes __________________
+.PP
+.B fsinfo_cap_xattrs
+.br
+.B fsinfo_cap_symlinks
+.br
+.B fsinfo_cap_hard_links
+.br
+.B fsinfo_cap_hard_links_1dir
+.br
+.B fsinfo_cap_device_files
+.br
+.B fsinfo_cap_unix_specials
+.IP
+These indicate that the filesystem supports respectively extended attributes;
+symbolic links; hard links spanning direcories; hard links, but only within a
+directory; block and character device files; and UNIX special files, such as
+FIFO and socket.
+
+.\" __________________ fsinfo_cap_*journal* __________________
+.PP
+.B fsinfo_cap_journal
+.br
+.B fsinfo_cap_data_is_journalled
+.IP
+The first of these indicates that the filesystem has a journal and the second
+that the file data changes are being journalled.
+
+.\" __________________ fsinfo_cap_o_* __________________
+.PP
+.B fsinfo_cap_o_sync
+.br
+.B fsinfo_cap_o_direct
+.IP
+These indicate that O_SYNC and O_DIRECT are supported respectively.
+
+.\" __________________ fsinfo_cap_o_* __________________
+.PP
+.B fsinfo_cap_volume_id
+.br
+.B fsinfo_cap_volume_uuid
+.br
+.B fsinfo_cap_volume_name
+.br
+.B fsinfo_cap_volume_fsid
+.br
+.B fsinfo_cap_cell_name
+.br
+.B fsinfo_cap_domain_name
+.br
+.B fsinfo_cap_realm_name
+.IP
+These indicate if various attributes are supported by the filesystem, where
+.B fsinfo_cap_X
+here corresponds to
+.BR fsinfo_attr_X .
+
+.\" __________________ fsinfo_cap_iver_* __________________
+.PP
+.B fsinfo_cap_iver_all_change
+.br
+.B fsinfo_cap_iver_data_change
+.br
+.B fsinfo_cap_iver_mono_incr
+.IP
+These indicate if
+.I i_version
+on an inode in the filesystem is supported and
+how it behaves.
+.B all_change
+indicates that i_version is incremented on metadata changes as well as data
+changes.
+.B data_change
+indicates that i_version is only incremented on data changes, including
+truncation.
+.B mono_incr
+indicates that i_version is incremented by exactly 1 for each change made.
+
+.\" __________________ fsinfo_cap_resource_forks __________________
+.TP
+.B fsinfo_cap_resource_forks
+This indicates that the filesystem supports some sort of resource fork or
+alternate data stream on a file. This isn't the same as an extended attribute.
+
+.\" __________________ fsinfo_cap_name_* __________________
+.PP
+.B fsinfo_cap_name_case_indep
+.br
+.B fsinfo_cap_name_non_utf8
+.br
+.B fsinfo_cap_name_has_codepage
+.IP
+These indicate certain facts about the filenames in a filesystem: whether
+they're case-independent; if they're not UTF-8; and if there's a codepage
+employed to map the names.
+
+.\" __________________ fsinfo_cap_sparse __________________
+.TP
+.B fsinfo_cap_sparse
+This indicates that the filesystem supports sparse files.
+
+.\" __________________ fsinfo_cap_not_persistent __________________
+.TP
+.B fsinfo_cap_not_persistent
+This indicates that the filesystem is not persistent, and that any data stored
+here will not be saved in the event that the filesystem is unmounted, the
+machine is rebooted or the machine loses power.
+
+.\" __________________ fsinfo_cap_no_unix_mode __________________
+.TP
+.B fsinfo_cap_no_unix_mode
+This indicates that the filesystem doesn't support the UNIX mode permissions
+bits.
+
+.\" __________________ fsinfo_cap_has_*time __________________
+.PP
+.B fsinfo_cap_has_atime
+.br
+.B fsinfo_cap_has_btime
+.br
+.B fsinfo_cap_has_ctime
+.br
+.B fsinfo_cap_has_mtime
+.IP
+These indicate as to what timestamps a filesystem supports, including: Access
+time, Birth/creation time, Change time (metadata and data) and Modification
+time (data only).
+
+
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.SH RETURN VALUE
+On success, the size of the value that the kernel has available is returned,
+irrespective of whether the buffer is large enough to hold that. The data
+written to the buffer will be truncated if it is not. On error, \-1 is
+returned, and
+.I errno
+is set appropriately.
+.SH ERRORS
+.TP
+.B EACCES
+Search permission is denied for one of the directories
+in the path prefix of
+.IR pathname .
+(See also
+.BR path_resolution (7).)
+.TP
+.B EBADF
+.I dirfd
+is not a valid open file descriptor.
+.TP
+.B EFAULT
+.I pathname
+is NULL or
+.IR pathname ", " params " or " buffer
+point to a location outside the process's accessible address space.
+.TP
+.B EINVAL
+Reserved flag specified in
+.IR params->at_flags " or one of " params->__reserved[]
+is not 0.
+.TP
+.B EOPNOTSUPP
+Unsupported attribute requested in
+.IR params->request .
+This may be beyond the limit of the supported attribute set or may just not be
+one that's supported by the filesystem.
+.TP
+.B ENODATA
+Unavailable attribute value requested by
+.IR params->Nth " and/or " params->Mth .
+.TP
+.B ELOOP
+Too many symbolic links encountered while traversing the pathname.
+.TP
+.B ENAMETOOLONG
+.I pathname
+is too long.
+.TP
+.B ENOENT
+A component of
+.I pathname
+does not exist, or
+.I pathname
+is an empty string and
+.B AT_EMPTY_PATH
+was not specified in
+.IR params->at_flags .
+.TP
+.B ENOMEM
+Out of memory (i.e., kernel memory).
+.TP
+.B ENOTDIR
+A component of the path prefix of
+.I pathname
+is not a directory or
+.I pathname
+is relative and
+.I dirfd
+is a file descriptor referring to a file other than a directory.
+.SH VERSIONS
+.BR fsinfo ()
+was added to Linux in kernel 4.18.
+.SH CONFORMING TO
+.BR fsinfo ()
+is Linux-specific.
+.SH NOTES
+Glibc does not (yet) provide a wrapper for the
+.BR fsinfo ()
+system call; call it using
+.BR syscall (2).
+.SH SEE ALSO
+.BR ioctl_iflags (2),
+.BR statx (2),
+.BR statfs (2)
diff --git a/man2/ioctl_iflags.2 b/man2/ioctl_iflags.2
index 9c77b08b9..49ba4444e 100644
--- a/man2/ioctl_iflags.2
+++ b/man2/ioctl_iflags.2
@@ -200,9 +200,15 @@ the effective user ID of the caller must match the owner of the file,
or the caller must have the
.BR CAP_FOWNER
capability.
+.PP
+The set of flags supported by a filesystem can be determined by calling
+.IR fsinfo (2)
+with attribute
+.IR fsinfo_attr_supports .
.SH SEE ALSO
.BR chattr (1),
.BR lsattr (1),
+.BR fsinfo (2),
.BR mount (2),
.BR btrfs (5),
.BR ext4 (5),
diff --git a/man2/stat.2 b/man2/stat.2
index dad9a01ac..ee4001f85 100644
--- a/man2/stat.2
+++ b/man2/stat.2
@@ -532,6 +532,12 @@ If none of the aforementioned macros are defined,
then the nanosecond values are exposed with names of the form
.IR st_atimensec .
.\"
+.PP
+Which timestamps are supported by a filesystem and their the ranges and
+granularities can be determined by calling
+.IR fsinfo (2)
+with attribute
+.IR fsinfo_attr_timestamp_info .
.SS C library/kernel differences
Over time, increases in the size of the
.I stat
@@ -707,6 +713,7 @@ main(int argc, char *argv[])
.BR access (2),
.BR chmod (2),
.BR chown (2),
+.BR fsinfo (2),
.BR readlink (2),
.BR utime (2),
.BR capabilities (7),
diff --git a/man2/statx.2 b/man2/statx.2
index edac9f6f4..9a57c1b90 100644
--- a/man2/statx.2
+++ b/man2/statx.2
@@ -534,12 +534,25 @@ Glibc does not (yet) provide a wrapper for the
.BR statx ()
system call; call it using
.BR syscall (2).
+.PP
+The sets of mask/stx_mask and stx_attributes bits supported by a filesystem
+can be determined by calling
+.IR fsinfo (2)
+with attribute
+.IR fsinfo_attr_supports .
+.PP
+Which timestamps are supported by a filesystem and their the ranges and
+granularities can also be determined by calling
+.IR fsinfo (2)
+with attribute
+.IR fsinfo_attr_timestamp_info .
.SH SEE ALSO
.BR ls (1),
.BR stat (1),
.BR access (2),
.BR chmod (2),
.BR chown (2),
+.BR fsinfo (2),
.BR readlink (2),
.BR stat (2),
.BR utime (2),
diff --git a/man2/utime.2 b/man2/utime.2
index 03a43a416..c6acdbac2 100644
--- a/man2/utime.2
+++ b/man2/utime.2
@@ -181,9 +181,16 @@ on an append-only file.
.\" is just a wrapper for
.\" .BR utime ()
.\" and hence does not allow a subsecond resolution.
+.PP
+Which timestamps are supported by a filesystem and their the ranges and
+granularities can be determined by calling
+.IR fsinfo (2)
+with attribute
+.IR fsinfo_attr_timestamp_info .
.SH SEE ALSO
.BR chattr (1),
.BR touch (1),
+.BR fsinfo (2),
.BR futimesat (2),
.BR stat (2),
.BR utimensat (2),
diff --git a/man2/utimensat.2 b/man2/utimensat.2
index d61b43e96..be8925548 100644
--- a/man2/utimensat.2
+++ b/man2/utimensat.2
@@ -633,9 +633,16 @@ instead checks whether the
.\" conversely, a process with a read-only file descriptor won't
.\" be able to update the timestamps of a file,
.\" even if it has write permission on the file.
+.PP
+Which timestamps are supported by a filesystem and their the ranges and
+granularities can be determined by calling
+.IR fsinfo (2)
+with attribute
+.IR fsinfo_attr_timestamp_info .
.SH SEE ALSO
.BR chattr (1),
.BR touch (1),
+.BR fsinfo (2),
.BR futimesat (2),
.BR openat (2),
.BR stat (2),
--
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