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.\"     @(#)fcntl.2	8.2 (Berkeley) 1/12/94
.\"
.Dd August 12, 2021
.Dt FCNTL 2
.Os BSD 4.2
.Sh NAME
.Nm fcntl
.Nd file control
.Sh SYNOPSIS
.Fd #include <fcntl.h>
.Ft int
.Fo fcntl
.Fa "int fildes"
.Fa "int cmd"
.Fa "..."
.Fc
.Sh DESCRIPTION
.Fn fcntl
provides for control over descriptors.
The argument
.Fa fildes
is a descriptor to be operated on by
.Fa cmd
as follows:
.Bl -tag -width F_GETPATH_NOFIRMLINKX
.It Dv F_DUPFD
Return a new descriptor as follows:
.Pp
.Bl -bullet -compact -offset 4n
.It
Lowest numbered available descriptor greater than or equal to
.Fa arg .
.It
Same object references as the original descriptor.
.It
New descriptor shares the same file offset if the object
was a file.
.It
Same access mode (read, write or read/write).
.It
Same file status flags (i.e., both file descriptors
share the same file status flags).
.It
The close-on-exec flag associated with the new file descriptor
is cleared so that the descriptor remains open across an
.Xr execv 2
system call.
.El
.It Dv F_DUPFD_CLOEXEC
Like
.Dv F_DUPFD ,
except that the close-on-exec flag associated with the new file descriptor
is set.
.It Dv F_GETFD
Get the flags associated with the file descriptor
.Fa fildes ,
as described below
.Fa ( arg
is ignored).
.It Dv F_SETFD
Set the file descriptor flags to
.Fa arg .
.It Dv F_GETFL
Get descriptor status flags, as described below
.Fa ( arg
is ignored).
.It Dv F_SETFL
Set descriptor status flags to
.Fa arg .
.It Dv F_GETOWN
Get the process ID or process group
currently receiving
.Dv SIGIO
and
.Dv SIGURG
signals; process groups are returned
as negative values
.Fa ( arg
is ignored).
.It Dv F_SETOWN
Set the process or process group
to receive
.Dv SIGIO
and
.Dv SIGURG
signals;
process groups are specified by supplying
.Fa arg
as negative, otherwise 
.Fa arg
is interpreted as a process ID.
.It Dv F_GETPATH
Get the path of the file descriptor
.Fa fildes .
The argument must be a buffer of size
.Sy MAXPATHLEN
or greater.
.It Dv F_GETPATH_NOFIRMLINK
Get the non firmlinked path of the file descriptor
.Fa fildes .
The argument must be a buffer of size
.Sy MAXPATHLEN
or greater.
.It Dv F_PREALLOCATE
Preallocate file storage space.
Note: upon success, the space that is allocated can be the size requested,
larger than the size requested, or (if the
.Dv F_ALLOCATEALL
flag is not provided) smaller than the space requested.
.It Dv F_PUNCHHOLE
Deallocate a region and replace it with a hole. Subsequent reads of the
affected region will return bytes of zeros that are usually not backed by
physical blocks. This will not change the actual file size. Holes must be
aligned to file system block boundaries. This will fail on
file systems that do not support this interface.
.It Dv F_SETSIZE
Deprecated.
In previous releases, this would allow a process with root privileges to
truncate a file without zeroing space.
For security reasons, this operation is no longer supported and will
instead truncate the file in the same manner as
.Xr truncate 2 .
.It Dv F_RDADVISE
Issue an advisory read async with no copy to user.
.It Dv F_RDAHEAD
Turn read ahead off/on.
A zero value in
.Fa arg
disables read ahead.
A non-zero value in
.Fa arg
turns read ahead on.
.It Dv F_NOCACHE
Turns data caching off/on. A non-zero value in
.Fa arg
turns data caching off.
A value of zero in
.Fa arg
turns data caching on.
.It Dv F_LOG2PHYS
Get disk device information.
Currently this only returns the
disk device address that corresponds
to the current file offset. Note that the system 
may return -1 as the disk device address if the file is not 
backed by physical blocks. This is subject
to change.
.It Dv F_LOG2PHYS_EXT
Variant of F_LOG2PHYS that uses the passed in
file offset and length.
.It Dv F_BARRIERFSYNC
Does the same thing as
.Xr fsync 2
then issues a barrier command to the drive
.Fa ( arg
is ignored).
The barrier applies to I/O that have been flushed with
.Xr fsync 2
on the same device before.  These operations are guaranteed to
be persisted before any other I/O that would follow the barrier,
although no assumption should be made on what has been persisted
or not when this call returns.  After the barrier has been issued,
operations on other FDs that have been fsync'd before can still be
re-ordered by the device, but not after the barrier.  This is
typically useful to guarantee valid state on disk when ordering is a
concern but durability is not.  A barrier can be used to order two phases of operations on
a set of file descriptors and ensure that no file can possibly get persisted
with the effect of the second phase without the effect of the first one. To do so,
execute operations of phase one, then
.Xr fsync 2
each FD and issue a single barrier.  Finally execute operations of phase two.
This is currently implemented on HFS and APFS. It requires hardware support,
which Apple SSDs are guaranteed to provide.
.It Dv F_FULLFSYNC
Does the same thing as
.Xr fsync 2
then asks the drive to
flush all buffered data to
the permanent storage device
.Fa ( arg
is ignored).
As this drains the entire queue of the device and acts as a
barrier, data that had been fsync'd on the same device before
is guaranteed to be persisted when this call returns.
This is currently implemented on HFS, MS-DOS (FAT),
Universal Disk Format (UDF) and APFS file systems.
The operation may take quite a while to complete.
Certain FireWire drives have also been known
to ignore the request to flush their buffered data.
.It Dv F_SETNOSIGPIPE
Determines whether a
.Dv SIGPIPE
signal will be generated when a write fails on a pipe or socket for
which there is no reader.  If
.Fa arg
is non-zero,
.Dv SIGPIPE
generation is disabled for descriptor
.Fa fildes ,
while an
.Fa arg
of zero enables it (the default).
.It Dv F_GETNOSIGPIPE
Returns whether a
.Dv SIGPIPE
signal will be generated when a write fails on a pipe or socket
for which there is no reader.  The semantics of the return value
match those of the
.Fa arg
of
.Dv F_SETNOSIGPIPE .
.It Dv F_TRANSFEREXTENTS
Transfer any extra space in the file past the logical EOF (as previously
allocated via
.Dv F_PREALLOCATE )
to another file.  The other file is specified via a file descriptor
as the lone extra argument.  Both descriptors must reference regular
files in the same volume.
.El
.Pp
The flags for the
.Dv F_GETFD
and
.Dv F_SETFD
commands are as follows:
.Bl -tag -width FD_CLOEXECX -offset indent
.It Dv FD_CLOEXEC
Close-on-exec; the given file descriptor will be automatically
closed in the successor process image when one of the
.Xr execv 2
or
.Xr posix_spawn 2
family of system calls is invoked.
.El
.Pp
The flags for the
.Dv F_GETFL
and
.Dv F_SETFL
commands are as follows:
.Bl -tag -width O_NONBLOCKX -offset indent
.It Dv O_NONBLOCK
Non-blocking I/O; if no data is available to a
.Xr read 2
call, or if a
.Xr write 2
operation would block,
the read or write call returns -1 with the error
.Er EAGAIN .
.It Dv O_APPEND
Force each write to append at the end of file;
corresponds to the
.Dv O_APPEND
flag of
.Xr open 2 .
.It Dv O_ASYNC
Enable the
.Dv SIGIO
signal to be sent to the process group
when I/O is possible, e.g.,
upon availability of data to be read.
.El
.Pp
Several commands are available for doing advisory file locking;
they all operate on the following structure:
.ne 7v
.Bd -literal
        struct flock {
	    off_t	l_start;    /* starting offset */
	    off_t	l_len;	    /* len = 0 means until end of file */
	    pid_t	l_pid;	    /* lock owner */
	    short	l_type;	    /* lock type: read/write, etc. */
	    short	l_whence;   /* type of l_start */
        };
.Ed
.Pp
The commands available for advisory record locking are as follows:
.Bl -tag -width F_SETLKWX
.It Dv F_GETLK
Get the first lock that blocks the lock description pointed to by the
third argument,
.Fa arg ,
taken as a pointer to a
.Fa "struct flock"
(see above).
The information retrieved overwrites the information passed to
.Nm fcntl
in the
.Fa flock
structure.
If no lock is found that would prevent this lock from being created,
the structure is left unchanged by this function call except for the
lock type which is set to
.Dv F_UNLCK .
If a lock that does not support the discovery of lock ownership by process
(such as an OFD lock (see below), one created by the
.Xr flock 2
system call or the
.Xr open 2
system call with the
.Dv O_SHLOCK
or
.Dv O_EXLOCK
flag) is found,
.Fa l_pid
is set to -1.
.It Dv F_SETLK
Set or clear a file segment lock according to the lock description
pointed to by the third argument,
.Fa arg ,
taken as a pointer to a
.Fa "struct flock"
(see above).
.Dv F_SETLK
is used to establish shared (or read) locks
.Dv (F_RDLCK)
or exclusive (or write) locks,
.Dv (F_WRLCK) ,
as well as remove either type of lock
.Dv (F_UNLCK) .
If a shared or exclusive lock cannot be set,
.Nm fcntl
returns immediately with
.Er EAGAIN .
.It Dv F_SETLKW
This command is the same as
.Dv F_SETLK
except that if a shared or exclusive lock is blocked by other locks,
the thread waits until the request can be satisfied.
If a signal that is to be caught is received while
.Nm fcntl
is waiting for a region, the
.Nm fcntl
will be interrupted if the signal handler has not specified the
.Dv SA_RESTART
(see
.Xr sigaction 2 ) .
.El
.Pp
When a shared lock has been set on a segment of a file,
other processes can set shared locks on that segment
or a portion of it.
A shared lock prevents any other process from setting an exclusive
lock on any portion of the protected area.
A request for a shared lock fails if the file descriptor was not
opened with read access.
.Pp
An exclusive lock prevents any other process from setting a shared lock or
an exclusive lock on any portion of the protected area.
A request for an exclusive lock fails if the file was not
opened with write access.
.Pp
The value of
.Fa l_whence
is
.Dv SEEK_SET ,
.Dv SEEK_CUR ,
or
.Dv SEEK_END
to indicate that the relative offset,
.Fa l_start
bytes, will be measured from the start of the file,
current position, or end of the file, respectively.
The value of
.Fa l_len
is the number of consecutive bytes to be locked.
If
.Fa l_len
is negative, the result is undefined.
The
.Fa l_pid
field is only used with
.Dv F_GETLK
to return the process ID of the process holding a blocking lock.
After a successful
.Dv F_GETLK
request, the value of
.Fa l_whence
is
.Dv SEEK_SET .
.Pp
Locks may start and extend beyond the current end of a file,
but may not start or extend before the beginning of the file.
A lock is set to extend to the largest possible value of the
file offset for that file if
.Fa l_len
is set to zero. If
.Fa l_whence
and
.Fa l_start
point to the beginning of the file, and
.Fa l_len
is zero, the entire file is locked.
If an application wishes only to do entire file locking, the
.Xr flock 2
system call is more efficient.
.Pp
There is at most one type of lock set for each byte in the file.
Before a successful return from an
.Dv F_SETLK
or an
.Dv F_SETLKW
request when the calling process has previously existing locks
on bytes in the region specified by the request,
the previous lock type for each byte in the specified
region is replaced by the new lock type.
As specified above under the descriptions
of shared locks and exclusive locks, an
.Dv F_SETLK
or an
.Dv F_SETLKW
request fails or blocks respectively when another process has existing
locks on bytes in the specified region and the type of any of those
locks conflicts with the type specified in the request.
.Pp
This interface follows the completely stupid semantics of System V and
.St -p1003.1-88
that require that all locks associated with a file for a given process are
removed when \fIany\fP file descriptor for that file is closed by that process.
This semantic means that applications must be aware of any files that
a subroutine library may access.
For example if an application for updating the password file locks the
password file database while making the update, and then calls
.Xr getpwnam 3
to retrieve a record,
the lock will be lost because 
.Xr getpwnam 3
opens, reads, and closes the password database.
The database close will release all locks that the process has
associated with the database, even if the library routine never
requested a lock on the database.
Another minor semantic problem with this interface is that
locks are not inherited by a child process created using the
.Xr fork 2
function.
The
.Xr flock 2
interface has much more rational last close semantics and
allows locks to be inherited by child processes.
.Xr Flock 2
is recommended for applications that want to ensure the integrity
of their locks when using library routines or wish to pass locks
to their children.
Note that 
.Xr flock 2
and 
.Nm fcntl
locks may be safely used concurrently.
.Pp
All locks associated with a file for a given process are
removed when the process terminates.
.Pp
A potential for deadlock occurs if a process controlling a locked region
is put to sleep by attempting to lock the locked region of another process.
This implementation detects that sleeping until a locked region is unlocked
would cause a deadlock and fails with an
.Er EDEADLK
error.
.Pp
An alternative set of commands is available for advisory record locking;
they operate on the same
.Fa flock
structure described above, the fields of the structure have the same
semantics, and the commands behave similarly to the traditional record
locks described above.
The primary difference is that
.Em open file description
(OFD) locks are locks on the file associated with the open file description
used to acquire them, and not with the process that created them.
OFD locks are conceptually similar to locks managed by
.Xr flock 2 ,
with the addition of record locking capabilities.
.Pp
A new open file description can be obtained from e.g.,
.Xr open 2 .
However, file descriptors that have been duplicated using e.g.,
.Xr dup 2
or
.Xr fork 2
do
.Sy not
result in multiple instances of a lock, but create additional
references to the same open file description, and thus reference the same lock.
For example, if a process holding an OFD lock on a file forks, and the child
explicitly unlocks a record, the parent will also lose that lock on the
same record.
.Pp
Only the last close of the last file descriptor in any process still
referencing the open file description causes an automatic unlock to occur,
so this type of record lock avoids the more unfortunate
.Xr close 2
semantics of traditional advisory record locks.
.Pp
The commands used for OFD locks are direct analogs of traditional
record locking commands:
.\"
.Bl -tag -width F_OFD_SETLKWX
.It Dv F_OFD_GETLK
Get the first lock that blocks the lock description pointed to by the
third argument,
.Fa arg ,
taken as a pointer to a
.Fa "struct flock"
(see above).
The information retrieved overwrites the information passed to
.Nm fcntl
in the
.Fa flock
structure.
If no lock is found that would prevent this lock from being created,
the structure is left unchanged by this function call except for the
lock type which is set to
.Dv F_UNLCK .
If a lock that does not support the discovery of lock ownership by process
(such as an OFD lock, one created by the
.Xr flock 2
system call or the
.Xr open 2
system call with the
.Dv O_SHLOCK
or
.Dv O_EXLOCK
flag) is found,
.Fa l_pid
is set to -1.
.\"
.It Dv F_OFD_SETLK
Set or clear a file segment lock according to the lock description
pointed to by the third argument,
.Fa arg ,
taken as a pointer to a
.Fa "struct flock"
(see above).
.Dv F_SETLK
is used to establish shared (or read) locks
.Dv (F_RDLCK)
or exclusive (or write) locks,
.Dv (F_WRLCK) ,
as well as remove either type of lock
.Dv (F_UNLCK) .
If a shared or exclusive lock cannot be set,
.Nm fcntl
returns immediately with a return value of -1.
.\"
.It Dv F_OFD_SETLKW
This command is the same as
.Dv F_OFD_SETLK
except that if a shared or exclusive lock is blocked by other locks,
the thread waits until the request can be satisfied.
If a signal that is to be caught is received while
.Nm fcntl
is waiting for a region, the
.Nm fcntl
will be interrupted if the signal handler has not specified the
.Dv SA_RESTART
(see
.Xr sigaction 2 ) .
.El
.\"
.Pp
No deadlock detection is performed for OFD file locks.
.\"
.Pp
The
.Dv F_PREALLOCATE
command operates on the following structure:
.ne 7v
.Bd -literal
        typedef struct fstore {
	    u_int32_t fst_flags;      /* IN: flags word */
	    int       fst_posmode;    /* IN: indicates offset field */
	    off_t     fst_offset;     /* IN: start of the region */
	    off_t     fst_length;     /* IN: size of the region */
	    off_t     fst_bytesalloc; /* OUT: number of bytes allocated */
        } fstore_t;
.Ed
.Pp
The flags (fst_flags) for the
.Dv F_PREALLOCATE
command are as follows:
.Bl -tag -width F_ALLOCATECONTIGX -offset indent
.It Dv F_ALLOCATECONTIG
Allocate contiguous space. (Note that the file system may ignore this request if
.Fa fst_length
is very large.)
.It Dv F_ALLOCATEALL
Allocate all requested space or no space at all.
.It Dv F_ALLOCATEPERSIST
Allocate space that is not freed when
.Xr close 2
is called. (Note that the file system may ignore this request.)
.El
.Pp
The position modes (fst_posmode) for the
.Dv F_PREALLOCATE
command indicate how to use the offset field.
The modes are as follows:
.Bl -tag -width F_PEOFPOSMODEX -offset indent
.It Dv F_PEOFPOSMODE
Allocate from the physical end of file.
In this case,
.Fa fst_length
indicates the number of newly allocated bytes desired.
.It Dv F_VOLPOSMODE
Allocate from the volume offset.
.El
.Pp
The
.Dv F_PUNCHHOLE
command operates on the following structure:
.ne 7v
.Bd -literal
        typedef struct fpunchhole {
            u_int32_t fp_flags;     /* unused */
            u_int32_t reserved;     /* (to maintain 8-byte alignment) */
            off_t     fp_offset;    /* IN: start of the region */
            off_t     fp_length;    /* IN: size of the region */
        } fpunchhole_t;
.Ed
.Pp
The
.Dv F_RDADVISE
command operates on the following structure
which holds information passed from the
user to the system:
.ne 7v
.Bd -literal
        struct radvisory {
           off_t   ra_offset;  /* offset into the file */
           int     ra_count;   /* size of the read     */
        };
.Ed
.Pp
The
.Dv F_LOG2PHYS
command operates on the following structure:
.ne 7v
.Bd -literal
        struct log2phys {
            u_int32_t l2p_flags;        /* unused so far */
            off_t     l2p_contigbytes;  /* unused so far */
            off_t     l2p_devoffset;    /* bytes into device */
        };
.Ed
.Pp
The
.Dv F_LOG2PHYS_EXT
command operates on the same structure as F_LOG2PHYS but treats it as an in/out:
.ne 7v
.Bd -literal
        struct log2phys {
            u_int32_t l2p_flags;        /* unused so far */
            off_t     l2p_contigbytes;  /* IN: number of bytes to be queried;
                                           OUT: number of contiguous bytes allocated at this position */
            off_t     l2p_devoffset;    /* IN: bytes into file;
                                           OUT: bytes into device */
        };
.Ed
.Pp
If
.Fa fildes
is a socket, then the
.Dv F_SETNOSIGPIPE
and
.Dv F_GETNOSIGPIPE
commands are directly analogous, and fully interoperate with the
.Dv SO_NOSIGPIPE
option of
.Xr setsockopt 2
and
.Xr getsockopt 2
respectively.
.Sh RETURN VALUES
Upon successful completion, the value returned depends on
.Fa cmd
as follows:
.Bl -tag -width F_GETOWNX -offset indent
.It Dv F_DUPFD
A new file descriptor.
.It Dv F_GETFD
Value of flag (only the low-order bit is defined).
.It Dv F_GETFL
Value of flags.
.It Dv F_GETOWN
Value of file descriptor owner.
.It other
Value other than -1.
.El
.Pp
Otherwise, a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn fcntl
system call will fail if:
.Bl -tag -width Er
.\" ==========
.It Bq Er EAGAIN
The argument
.Fa cmd
is
.Dv F_SETLK
or
.Dv F_OFD_SETLK ,
the type of lock
.Fa (l_type)
is a shared lock
.Dv (F_RDLCK)
or exclusive lock
.Dv (F_WRLCK) ,
and the segment of a file to be locked is already
exclusive-locked by another process;
or the type is an exclusive lock and some portion of the
segment of a file to be locked is already shared-locked or
exclusive-locked by another process.
.It Bq Er EACCES
The argument
.Fa cmd
is
.Dv F_SETSIZE
and the calling process does not have root privileges.
.\" ==========
.It Bq Er EBADF
.Fa Fildes
is not a valid open file descriptor.
.Pp
The argument
.Fa cmd
is
.Dv F_SETLK ,
.Dv F_SETLKW ,
.Dv F_OFD_SETLK
or
.Dv F_OFD_SETLKW ,
the type of lock
.Fa (l_type)
is a shared lock
.Dv (F_RDLCK) ,
and
.Fa fildes
is not a valid file descriptor open for reading.
.Pp
The argument
.Fa cmd
is
.Dv F_SETLK ,
.Dv F_SETLKW ,
.Dv F_OFD_SETLK
or
.Dv F_OFD_SETLKW ,
the type of lock
.Fa (l_type)
is an exclusive lock
.Dv (F_WRLCK) ,
and
.Fa fildes
is not a valid file descriptor open for writing.
.Pp
The argument
.Fa cmd
is
.Dv F_PREALLOCATE
and the calling process does not have
file write permission.
.Pp
The argument
.Fa cmd
is
.Dv F_LOG2PHYS
or
.Dv F_LOG2PHYS_EXT
and
.Fa fildes
is not a valid file descriptor open for reading.
.Pp
The argument
.Fa cmd
is
.Dv F_TRANSFEREXTENTS
and either file descriptor does not correspond to a valid
regular file, or either file is not open for writing.
.\" ==========
.It Bq Er EDEADLK
The argument
.Fa cmd
is
.Dv F_SETLKW ,
and a deadlock condition was detected.
.\" ==========
.It Bq Er EFBIG
The argument
.Fa cmd
is
.Dv F_PREALLOCATE ,
.Dv F_PEOFPOSMODE
is set and preallocating
.Fa fst_length
bytes on
.Fa fildes
would exceed the maximum file size.
.\" ==========
.It Bq Er EINTR
The argument
.Fa cmd
is
.Dv F_SETLKW
or
.Dv F_OFD_SETLKW ,
and the function was interrupted by a signal.
.\" ==========
.It Bq Er EINVAL
.Fa Cmd
is
.Dv F_DUPFD
and
.Fa arg
is negative or greater than the maximum allowable number
(see
.Xr getdtablesize 2 ) .
.Pp
The argument
.Fa cmd
is
.Dv F_GETLK ,
.Dv F_SETLK ,
.Dv F_SETLKW ,
.Dv F_OFD_GETLK ,
.Dv F_OFD_SETLK
or
.Dv F_OFD_SETLKW ,
and the data to which
.Fa arg
points is not valid, or
.Fa fildes
refers to a file that does not support locking.
.Pp
The argument
.Fa cmd
is
.Dv F_PREALLOCATE
and the
.Fa fst_posmode
is not a valid mode,
or when
.Dv F_PEOFPOSMODE
is set and
.Fa fst_offset
is a non-zero value,
or when
.Dv F_VOLPOSMODE
is set and
.Fa fst_offset
is a negative or zero value.
.Pp
The argument
.Fa cmd
is
.Dv F_PUNCHHOLE
and
either
.Fa fp_offset
or
.Fa fp_length
are negative, or when both
.Fa fp_offset
and
.Fa fp_length
are not multiples of the file system block size, or when either
.Fa fp_flags
or
.Fa reserved
is non-zero value.
.Pp
The argument
.Fa cmd
is
.Dv F_TRANSFEREXTENTS
and the additional file descriptor is negative or both file
descriptors reference the same file.
.\" ==========
.It Bq Er EMFILE
.Fa Cmd
is
.Dv F_DUPFD
and the maximum allowed number of file descriptors are currently
open.
.\" ==========
.It Bq Er EMFILE
The argument
.Fa cmd
is
.Dv F_DUPFD
and the maximum number of file descriptors permitted for the
process are already in use,
or no file descriptors greater than or equal to
.Fa arg
are available.
.\" ==========
.It Bq Er ENOLCK
The argument
.Fa cmd
is
.Dv F_SETLK ,
.Dv F_SETLKW ,
.Dv F_OFD_SETLK
or
.Dv F_OFD_SETLKW ,
and satisfying the lock or unlock request would result in the
number of locked regions in the system exceeding a system-imposed limit.
.\" ==========
.It Bq Er ENOSPC
The argument
.Fa cmd
is
.Dv F_PREALLOCATE
and either there is no space available on the volume containing
.Fa fildes
or
.Fa fst_flags
contains
.Dv F_ALLOCATEALL
and there is not enough space available on the volume containing
.Fa fildes
to satisfy the entire request.
.Pp
The argument
.Fa cmd
is
.Dv F_PUNCHHOLE
and there is not enough space available on the volume containing
.Fa fildes
to satisfy the request. As an example, a filesystem that supports
cloned files may return this error if punching a hole requires the
creation of a clone and there is not enough space available to do so.
.\" ==========
.It Bq Er EOVERFLOW
A return value would overflow its representation.
For example,
.Fa cmd
is F_GETLK, F_SETLK, or F_SETLKW
and the smallest (or, if l_len is non-zero, the largest) offset
of a byte in the requested segment
will not fit in an object of type off_t.
.\" ==========
.It Bq Er EPERM
The argument cmd is
.Dv F_PUNCHHOLE
and the calling process does not have file write permission.
.\" ==========
.It Bq Er EPERM
The argument cmd is
.Dv F_SETSIZE
and the named file has its append-only flag set, see the
.Xr chflags 2
manual page for more information.
.\" ==========
.It Bq Er EPERM
The argument cmd is
.Dv F_SETFL
and O_APPEND flag is not present but the named file has its append-only flag set.
.\" ==========
.It Bq Er ESRCH
.Fa Cmd
is
.Dv F_SETOWN
and
the process ID given as argument is not in use.
.\" ==========
.It Bq Er ENOTSUP
.Fa Cmd
is
.Dv F_TRANSFEREXTENTS
and the given files aren't on an APFS volume.
.\" ==========
.It Bq Er EXDEV
.Fa Cmd
is
.Dv F_TRANSFEREXTENTS
and the referenced files are not in the same volume.
.El
.Sh SEE ALSO
.Xr close 2 ,
.Xr execve 2 ,
.Xr flock 2 ,
.Xr fork 2 ,
.Xr getdtablesize 2 ,
.Xr open 2 ,
.Xr pipe 2 ,
.Xr setsockopt 2 ,
.Xr socket 2 ,
.Xr sigaction 3
.Sh HISTORY
The
.Fn fcntl
function call appeared in
.Bx 4.2 .
.Pp
Open file description locks first appeared in Linux 3.15