Hello David, As noted in another mail, I will ping on all of the mails, just to raise all the patches to the top of the inbox. Thanks, Michael On Thu, 27 Aug 2020 at 13:05, Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > > Hello David, > > On 8/24/20 2:24 PM, David Howells wrote: > > Add a manual page to document the fspick() system call. > > > > Signed-off-by: David Howells <dhowells@xxxxxxxxxx> > > --- > > > > man2/fspick.2 | 180 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 180 insertions(+) > > create mode 100644 man2/fspick.2 > > > > diff --git a/man2/fspick.2 b/man2/fspick.2 > > new file mode 100644 > > index 000000000..72bf645dd > > --- /dev/null > > +++ b/man2/fspick.2 > > @@ -0,0 +1,180 @@ > > +'\" t > > +.\" Copyright (c) 2020 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 +.\" manual page may be incorrect or out-of-date.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 FSPICK 2 2020-08-24 "Linux" "Linux Programmer's Manual" > > +.SH NAME > > +fspick \- Select filesystem for reconfiguration > > +.SH SYNOPSIS > > +.nf > > +.B #include <sys/types.h> > > +.B #include <sys/mount.h> > > +.B #include <unistd.h> > > +.BR "#include <fcntl.h> " "/* Definition of AT_* constants */" > > +.PP > > +.BI "int fspick(int " dirfd ", const char *" pathname ", unsigned int " flags ); > > +.fi > > +.PP > > +.IR Note : > > +There is no glibc wrapper for this system call. > > +.SH DESCRIPTION > > +.PP > > +.BR fspick () > > +creates a new filesystem configuration context within the kernel and attaches a > > +pre-existing superblock to it so that it can be reconfigured (similar to > > +.BR mount (8) > > +with the "-o remount" option). The configuration context is marked as being in > > +reconfiguration mode and attached to a file descriptor, which is returned to > > +the caller. The file descriptor can be marked close-on-exec by setting > > +.B FSPICK_CLOEXEC > > +in > > +.IR flags . > > +.PP > > +The target is whichever superblock backs the object determined by > > +.IR dfd ", " pathname " and " flags . > > +The following can be set in > > +.I flags > > +to control the pathwalk to that object: > > +.TP > > +.B FSPICK_SYMLINK_NOFOLLOW > > +Don't follow symbolic links in the final component of the path. > > +.TP > > +.B FSPICK_NO_AUTOMOUNT > > +Don't follow automounts in the final component of the path. > > +.TP > > +.B FSPICK_EMPTY_PATH > > +Allow an empty string to be specified as the pathname. This allows > > +.I dirfd > > +to specify the target mount exactly. > > +.PP > > +After calling fspick(), the file descriptor should be passed to the > > +.BR fsconfig (2) > > +system call, using that to specify the desired changes to filesystem and > > Better: s/using that/in order/ > > > +security parameters. > > +.PP > > +When the parameters are all set, the > > +.BR fsconfig () > > +system call should then be called again with > > +.B FSCONFIG_CMD_RECONFIGURE > > +as the command argument to effect the reconfiguration. > > +.PP > > +After the reconfiguration has taken place, the context is wiped clean (apart > > +from the superblock attachment, which remains) and can be reused to make > > +another reconfiguration. > > +.PP > > +The file descriptor also serves as a channel by which more comprehensive error, > > +warning and information messages may be retrieved from the kernel using > > +.BR read (2). > > +.SS Message Retrieval Interface > > +The context file descriptor may be queried for message strings at any time by > > s/descriptor/descriptor returned by fspick()/ > > > +calling > > +.BR read (2) > > +on the file descriptor. This will return formatted messages that are prefixed > > +to indicate their class: > > +.TP > > +\fB"e <message>"\fP > > +An error message string was logged. > > +.TP > > +\fB"i <message>"\fP > > +An informational message string was logged. > > +.TP > > +\fB"w <message>"\fP > > +An warning message string was logged. > > +.PP > > +Messages are removed from the queue as they're read and the queue has a limited > > +depth of 8 messages, so it's possible for some to get lost. > > What if there are no pending error messages to retrieve? What does > read() do in that case? Please add an explanation here. > > > +.SH RETURN VALUE > > +On success, the function returns a file descriptor. On error, \-1 is returned, > > +and > > +.I errno > > +is set appropriately. > > +.SH ERRORS > > +The error values given below result from filesystem type independent errors. > > +Additionally, each filesystem type may have its own special errors and its own > > +special behavior. See the Linux kernel source code for details. > > +.TP > > +.B EACCES > > +A component of a path was not searchable. > > +(See also > > +.BR path_resolution (7).) > > +.TP > > +.B EFAULT > > +.I pathname > > +points outside the user address space. > > +.TP > > +.B EINVAL > > +.I flags > > +includes an undefined value. > > +.TP > > +.B ELOOP > > +Too many links encountered during pathname resolution. > > +.TP > > +.B EMFILE > > +The system has too many open files to create more. > > +.TP > > +.B ENFILE > > +The process has too many open files to create more. > > +.TP > > +.B ENAMETOOLONG > > +A pathname was longer than > > +.BR MAXPATHLEN . > > MAXPATHLEN is not, I think, a constant known in user space. What is this? > Should it be PATH_MAX? > > > +.TP > > +.B ENOENT > > +A pathname was empty or had a nonexistent component. > > +.TP > > +.B ENOMEM > > +The kernel could not allocate sufficient memory to complete the call. > > +.TP > > +.B EPERM > > +The caller does not have the required privileges. > > Please note the necessary capability here. Also, there was no mention of > capabilities/privileges in DESCRIPTION. Should there have been? > > > +.SH CONFORMING TO > > +These functions are Linux-specific and should not be used in programs intended > > +to be portable. > > +.SH VERSIONS > > +.BR fsopen "(), " fsmount "() and " fspick () > > +were added to Linux in kernel 5.2. > > +.SH EXAMPLES > > +To illustrate the process, here's an example whereby this can be used to > > +reconfigure a filesystem: > > +.PP > > +.in +4n > > +.nf > > +sfd = fspick(AT_FDCWD, "/mnt", FSPICK_NO_AUTOMOUNT | FSPICK_CLOEXEC); > > +fsconfig(sfd, FSCONFIG_SET_FLAG, "ro", NULL, 0); > > +fsconfig(sfd, FSCONFIG_SET_STRING, "user_xattr", "false", 0); > > +fsconfig(sfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0); > > +.fi > > +.in > > +.PP > > +.SH NOTES > > +Glibc does not (yet) provide a wrapper for the > > +.BR fspick "()" > > +system call; call it using > > +.BR syscall (2). > > +.SH SEE ALSO > > +.BR mountpoint (1), > > +.BR fsconfig (2), > > +.BR fsopen (2), > > +.BR path_resolution (7), > > +.BR mount (8) > > Thanks, > > Michael > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/ -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
