New: Documentation misses case of symlink, symlinkat giving ENOENT for a directory with a reference only held by a process
https://bugzilla.kernel.org/show_bug.cgi?id=73301
Bug ID: 73301
Summary: Documentation misses case of symlink, symlinkat giving
ENOENT for a directory with a reference only held by a process
Product: Documentation
Version: unspecified
Hardware: All
OS: Linux
Status: NEW
Severity: low
Priority: P1
Component: man-pages
Assignee: documentation_man-pages-ztI5WcYan/[email protected]
Reporter: [email protected]
Regression: No
The errors printed out by the following code on symlink and symlinkat are missed by the documentation.
#include <fcntl.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
int main() {
if (-1 == mkdir("/tmp/temporary", S_IRWXU)) {
perror("mkdir");
}
int dir = open("/tmp/temporary", O_RDONLY | O_CLOEXEC);
if (-1 == dir) {
perror("open");
}
if (-1 == rmdir("/tmp/temporary")) {
perror("rmdir");
}
if (-1 == symlinkat("/", dir, "root")) {
perror("symlinkat");
}
char template_text[] = "/proc/self/fd/XXXXXXXXXXX/root";
sprintf(template_text, "/proc/self/fd/%i/root", dir);
if (-1 == symlink("/", template_text)) {
perror("symlink");
}
return 0;
}The calls to symlink and symlinkat in this case give ENOENT errors. This might also be a small oversight which is probably impossible to change now. I wonder if the code thinks this is a dangling symbolic link (a case which is mentioned by the documentation)?
The POSIX standard issue 7 also seems to miss this corner case (although it might simply be an omission of mentioning a system dependant case rather than a bug for the POSIX standard).
I'm not sure how exactly one would explain this corner case in the documentation.
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[Bug 73301] Documentation misses case of symlink, symlinkat giving ENOENT for a directory with a reference only held by a process
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=73301
--- Comment #1 from Steven Stewart-Gallus <[email protected]> --- This problem also exists with link and linkat.
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[Bug 73301] Documentation misses case of link, linkat, symlink, symlinkat giving ENOENT for a directory with a reference only held by a process
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=73301
Steven Stewart-Gallus <[email protected]> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|Documentation misses case |Documentation misses case
|of symlink, symlinkat |of link, linkat, symlink,
|giving ENOENT for a |symlinkat giving ENOENT for
|directory with a reference |a directory with a
|only held by a process |reference only held by a
| |processSignature · 6 lines
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[Bug 73301] Documentation misses case of link, linkat, symlink, symlinkat giving ENOENT for a directory with a reference only held by a process
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=73301
Michael Kerrisk <[email protected]> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |[email protected]
--- Comment #2 from Michael Kerrisk <[email protected]> --- Steven,
(In reply to Steven Stewart-Gallus from comment #0)
Quoted 19 lines
The errors printed out by the following code on symlink and symlinkat are missed by the documentation.
#include <
fcntl.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>int main() { if (-1 == mkdir("/tmp/temporary", S_IRWXU)) { perror("mkdir"); } int dir = open("/tmp/temporary", O_RDONLY | O_CLOEXEC); if (-1 == dir) { perror("open"); }
Quoted 7 lines
if (-1 == rmdir("/tmp/temporary")) {
perror("rmdir");
}
if (-1 == symlinkat("/", dir, "root")) {
perror("symlinkat");
}So far, so good.
Quoted 5 lines
char template_text[] = "/proc/self/fd/XXXXXXXXXXX/root";
sprintf(template_text, "/proc/self/fd/%i/root", dir);
if (-1 == symlink("/", template_text)) {
perror("symlink");
}I'm a little puzzled, why would one want to make a symlink somewhere under /proc?
Quoted 5 lines
return 0; }The calls to symlink and symlinkat in this case give ENOENT errors.
For symlinkat(), I can see the logic. You're trying to create a link relative to a directory that does not exist. Could the call reasonably do anything other than fail?
Quoted 8 lines
This
might also be a small oversight which is probably impossible to change now. I wonder if the code thinks this is a dangling symbolic link (a case which is mentioned by the documentation)?The POSIX standard issue 7 also seems to miss this corner case (although it might simply be an omission of mentioning a system dependant case rather than a bug for the POSIX standard).
The specs in POSIX were driven from the Linux implementation effort, so I don;t think that your hypothesis there would fit.
Quoted 2 lines
I'm not sure how exactly one would explain this corner case in the documentation.
I'd be willing to give it a shot, but, first,I'm not sure what if anything to say about the symlink() case. Do you have a more realistic example of that case?
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[Bug 73301] Documentation misses case of link, linkat, symlink, symlinkat giving ENOENT for a directory with a reference only held by a process
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=73301
--- Comment #3 from Steven Stewart-Gallus <[email protected]> --- On further reflection, this is not a problem with the documentation of
symlink, symlinkat, link and linkat but a problem with the
documentation of ENOENT and what a nonexisting directory actually
means.
I suppose how one might describe the situation is that when a directory is unlinked from a filesystem (but still has process references to it) it enters a zombie state where many filesystem calls become inappropriate to use on it.
I'm not sure where such documentation should be placed. We already have shm_overview(7), mq_overview(7) and such; and I think if we had a dir_overview(7) that would be the perfect place to put this corner case. dir_overview(7) might be too big project for not really any gain though.
Quoted 3 lines
I'd be willing to give it a shot, but, first,I'm not sure what if anything to say about the
symlink()case. Do you have a more realistic example of that case?
Nope. People should probably be able to figure that out from the description of the symlink case. I was just pointing it out for completeness and I'd be fine if that case was omitted.
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[Bug 73301] Documentation misses case of link, linkat, symlink, symlinkat giving ENOENT for a directory with a reference only held by a process
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=73301
Michael Kerrisk <[email protected]> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |CODE_FIX--- Comment #4 from Michael Kerrisk <[email protected]> --- I've applied the patches below.
man2/link.2 +11 -0
@@ -291,6 +291,17 @@ file corresponding to a file descriptor created with See .BR open (2). .TP +.B ENOENT +.I oldpath +is a relative pathname and +.I olddirfd +refers to a directory that has been deleted, +or +.I newpath +is a relative pathname and +.I newdirfd +refers to a directory that has been deleted. +.TP .B ENOTDIR .I oldpath is relative and
man2/symlink.2 +6 -0
@@ -210,6 +210,12 @@ The following additional errors can occur for .I newdirfd is not a valid file descriptor. .TP +.B ENOENT +.I linkpath +is a relative pathname and +.IR newdirfd +refers to a directory that has been deleted. +.TP .B ENOTDIR .I linkpath is relative and
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