Changes from v1: - Fallback to BUFSIZ if fstat fails instead of exiting. - Add a comment block to explain why the blksize is used in file_lines() (which I hope also clarifies why it is not needed elsewhere). - Only use blksize if it is > BUFSIZ (I had regressed to 4K reads, oops). - Update comments to reference bufsize instead of BUFSIZ. - Update subject because /proc is not affected, and it isn't limited to follow mode. - Add a test.
* src/tail.c (file_lines): Consider a full blocksize when searching backwards to find sysfs file content on systems with large page sizes. * tests/tail/tail-1-sysfs.sh: Add a new test. * tests/local.mk: Reference the new test. Fixes https://bugs.gnu.org/67490 --- src/tail.c | 41 +++++++++++++++++++++++++++----------- tests/local.mk | 1 + tests/tail/tail-1-sysfs.sh | 31 ++++++++++++++++++++++++++++ 3 files changed, 61 insertions(+), 12 deletions(-) create mode 100755 tests/tail/tail-1-sysfs.sh diff --git a/src/tail.c b/src/tail.c index c45f3b65a..f3219757d 100644 --- a/src/tail.c +++ b/src/tail.c @@ -518,19 +518,32 @@ static bool file_lines (char const *pretty_filename, int fd, uintmax_t n_lines, off_t start_pos, off_t end_pos, uintmax_t *read_pos) { - char buffer[BUFSIZ]; + char *buffer; size_t bytes_read; + blksize_t bufsize = BUFSIZ; off_t pos = end_pos; + bool ok = true; + struct stat stats; if (n_lines == 0) return true; + if (fstat (fd, &stats) == 0) + /* sysfs files have a blksize == kernel page size, which can be > BUFSIZ. + lseek SEEK_END moves to the next page, which is likely more than + BUFSIZ away from the end of the actual data. Use a buffer large enough + to hold an entire page, so that the window we search for data is large + enough to find it. */ + bufsize = MAX(BUFSIZ, ST_BLKSIZE (stats)); + + buffer = xmalloc (bufsize); + /* Set 'bytes_read' to the size of the last, probably partial, buffer; - 0 < 'bytes_read' <= 'BUFSIZ'. */ - bytes_read = (pos - start_pos) % BUFSIZ; + 0 < 'bytes_read' <= 'bufsize'. */ + bytes_read = (pos - start_pos) % bufsize; if (bytes_read == 0) - bytes_read = BUFSIZ; - /* Make 'pos' a multiple of 'BUFSIZ' (0 if the file is short), so that all + bytes_read = bufsize; + /* Make 'pos' a multiple of 'bufsize' (0 if the file is short), so that all reads will be on block boundaries, which might increase efficiency. */ pos -= bytes_read; xlseek (fd, pos, SEEK_SET, pretty_filename); @@ -538,7 +551,8 @@ file_lines (char const *pretty_filename, int fd, uintmax_t n_lines, if (bytes_read == SAFE_READ_ERROR) { error (0, errno, _("error reading %s"), quoteaf (pretty_filename)); - return false; + ok = false; + goto free_buffer; } *read_pos = pos + bytes_read; @@ -565,7 +579,7 @@ file_lines (char const *pretty_filename, int fd, uintmax_t n_lines, xwrite_stdout (nl + 1, bytes_read - (n + 1)); *read_pos += dump_remainder (false, pretty_filename, fd, end_pos - (pos + bytes_read)); - return true; + goto free_buffer; } } @@ -577,23 +591,26 @@ file_lines (char const *pretty_filename, int fd, uintmax_t n_lines, xlseek (fd, start_pos, SEEK_SET, pretty_filename); *read_pos = start_pos + dump_remainder (false, pretty_filename, fd, end_pos); - return true; + goto free_buffer; } - pos -= BUFSIZ; + pos -= bufsize; xlseek (fd, pos, SEEK_SET, pretty_filename); - bytes_read = safe_read (fd, buffer, BUFSIZ); + bytes_read = safe_read (fd, buffer, bufsize); if (bytes_read == SAFE_READ_ERROR) { error (0, errno, _("error reading %s"), quoteaf (pretty_filename)); - return false; + ok = false; + goto free_buffer; } *read_pos = pos + bytes_read; } while (bytes_read > 0); - return true; +free_buffer: + free (buffer); + return ok; } /* Print the last N_LINES lines from the end of the standard input, diff --git a/tests/local.mk b/tests/local.mk index a5fb62d96..af41337b1 100644 --- a/tests/local.mk +++ b/tests/local.mk @@ -257,6 +257,7 @@ all_tests = \ tests/seq/seq-precision.sh \ tests/head/head.pl \ tests/head/head-elide-tail.pl \ + tests/tail/tail-1-sysfs.sh \ tests/tail/tail-n0f.sh \ tests/ls/ls-misc.pl \ tests/date/date.pl \ diff --git a/tests/tail/tail-1-sysfs.sh b/tests/tail/tail-1-sysfs.sh new file mode 100755 index 000000000..078366588 --- /dev/null +++ b/tests/tail/tail-1-sysfs.sh @@ -0,0 +1,31 @@ +#!/bin/sh +# sysfs files have weird properties that can be influenced by page size + +# Copyright 2023 Free Software Foundation, Inc. + +# This program is free software: you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation, either version 3 of the License, or +# (at your option) any later version. + +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. + +# You should have received a copy of the GNU General Public License +# along with this program. If not, see <https://www.gnu.org/licenses/>. + +. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src +print_ver_ tail + +file=/sys/kernel/profiling + +if test -r $file; then + cp -f $file exp || framework_failure_ + tail -1 $file > out || fail=1 + + compare exp out || fail=1 +fi + +Exit $fail -- 2.43.0
